Machinable anisotropic permanent magnets of Mn-Al-C alloys

ABSTRACT

An anisotropic permanent magnet of an Mn-Al-C alloy containing 68.0% to 73.0% by weight of manganese, (1/10 Mn-6.6)% to (1/3 Mn-22.2)% by weight of carbon, and the remainder aluminum, which alloy is rendered anisotropic by deforming it plastically at a temperature of 530°C to 830°C. 
     The permanent magnet has excellent mechanical characteristics and magnetic properties such that the (BH)max is above 4.8 × 10 6  G.Oe up to about 9.2 × 10 6  G.Oe in its bulk state.

BACKGROUND OF THE INVENTION

This invention relates to permanent magnets and more particularly toanisotropic permanent magnets of manganese-aluminum-carbon (Mn-Al-C)alloys.

Previously known Mn-Al alloy magnets consisting of Mn 60-75 weight %(hereinafter referred to simply as %) and the remainder aluminum aresuch that the ferromagnetic metastable phase (face-centered tetragonal,lattice constant a = 3.94A, c = 3.58A, c/a = 0.908 and a Curie point of350° to 400°C; hereinafter referred to as the τ phase) is obtained byway of a heat treatment such as by the cooling control method or thequenching-tempering method. The ferromagnetic τ phase is the metastablephase which appears between the high temperature phase (close-packedhexagonal, lattice constant a = 2.69A, c = 4.38A; hereinafter referredto as the ε phase) and the room temperature phase (a phase in which thealloy is separated into the AlMn(γ) phase and the β-Mn phase). Thisintermediate phase was discovered by Nagasaki, Kono, and Hirone in 1955.(Digest of the Tenth Annual Conference of the Physical Society of Japan,Vol. 3, 162, October, 1955.)

However, the above Mn-Al alloys possess magnetic characteristics whichare low, i.e. in the order of (BH)max = 0.5 × 10⁶ G.Oe, Br = 2200 G, and_(B) Hc = 600 Oe. Since then, a method has been developed of sinteringthe powdered alloy in the τ phase whereby the coercive force isincreased by pulverizing; however, the magnetic characteristics of thesealloys in isotropic form, at best, were low, being in the order of(BH)max = 0.6 × 10⁶ G.Oe, Br = 1700 G, and _(B) Hc = 1250 Oe. Moreover,since the products were formed from powder, their mechanical strengthswere low, which makes these products impractical for commercial use.

On the other hand, a method has been proposed for improving the magneticcharacteristics of these Mn-Al alloy magnets by applying a high degreeof cold-working on the alloy in the τ phase (ferromagnetic phase) torender them anisotropic. It is known that rod shaped Mn-Al magnets inthe τ phase are sealed in nonmagnetic stainless steel pipes, and whilebeing held in said pipes are subjected to cold-working, such asswagining, to a degree of 85-95%. This method is capable of producing ananisotropic permanent magnet possessing magnetic characteristics in theorder of Br = 4280G, _(B) HC = 2700 Oe, and (BH)max ≈ 3.5 × 10⁶ G.Oe inthe direction of preferred magnetization, i.e., the axial direction ofthe rod. Because Mn-Al alloy magnets are intermetallic compounds havingvery hard and brittle mechanical properties, however, even acold-working of less than 1% causes cracks or fractures in the alloys.

On the other hand, since the degree of anisotropization is dependentupon the degree of cold-working, it is necessary to cold-work the alloyto a high degree, normally higher than 80%, in order to achievesatisfactory magnetic characteristics, and in order to be able toconduct such cold-working step, the cold-workig operation must beconducted while the alloy is sealed in a nonmagnetic stainless steelpipe.

An anisotropic permanent magnetic obtained by using the above method iscomplicated in that the Mn-Al alloy inside the pipe must be finelypulverized into powder, and, moreover, it is difficult to obtain rods ofuniform cross-section. The method is therefor costly and of littlepractical value.

In order to overcome the above difficulties, a method has been proposedof obtaining a rod shaped anisotropic Mn-Al alloy magnet by subjectingthe τ phase of the Mn-Al alloy magnet to hydrostatic extrusion at atemperature below 200°C, but the magnetic characteristic of such alloysis low, being in the order of (BH)max = 2.5-3.6 × 10⁶ G.Oe in thedirection of preferred magnetization. This method also requires a veryintricate hydrostatic extrusion operation and is again a veryimpractical method.

To replace the Mn-Al alloy magnets mentioned above, there have beeninvented manganese-aluminum-carbon alloy magnets in bulk shape havingexcellent magnetically isotropic characteristics, which magnets weredisclosed in U.S. Pat. No. 3,661,567. Thus, according to U.S. Pat. No.3,661,567, the Mn-Al-C alloy magnets may be obtained as isotropicpermanent magnets in bulk shape excelling in magnetic characteristics,stability, weathering resistance and mechanical strength. These alloysmay be mult-component alloys containing impurities or additives otherthan Mn, Al and C, but should contain Mn, Al, and C as indispensablecomponent elements, with the component ratio of Mn, Al, and C in thesemulti-component alloys falling within the following range:

             Mn  69.5˜73.0%                                                          Al  26.4˜29.5%                                                          C   0.6˜(1/3 Mn-22.2)%                                     

which alloys are manufactured under the restricted conditions describedhereinunder:

Thus, Mn. Al and C are so mixed that each component falls within therespective composition range mentioned above, then the mixture is heatedto a temperature higher than 1,380°C but lower than 1,500°C, in order toobtain a homogeneous melt with carbon forcibly dissolved therein, andthereafter the molten alloy is cast in a suitable mold. The ingotthus-obtained is heated above 900°C to form its high temperature phase,and then, is quenched by rapidly cooling it from a temperature above900°C to a temperature below 600°C at a cooling rate of higher than300°C/min. The quenched alloy is then tempered by heating it at atemperature of 480°-650°C. for an appropriate period of time. A Mn-Al-Calloy magnet in bulk shape obtained in this way has magneticcharacteristics better than (BH)max = 1.0 × 10⁶ G.Oe, while in anisotropic state. This magnetic characteristic runs twice as high as themagnetic characteristics of isotropic Mn-Al alloy magnets.

The Mn-Al-C alloy magnets obtained in this way were isotropic in theirbulk state, with the (BH)max running higher than 1.0 × 10⁶ G.Oe, andtheir mechanical strengths were as follows: hardness H_(RC) = 45,tensile strength = 1-2 kg/mm², elongation = 0, compressive strength =100 kg/mm², and transverse strength = 7 kg/mm².

The Mn-Al-C alloy magnets had serious disadvantages, however, in that inthe course of trying to further improve their magnetic characteristics;by whichever method of the above mentioned cold working method or thepowder forming method, the magnetis characteristics may be barelyimproved or rather degraded, and any improvement in their performance byway of anisotropization could not be anticipated.

SUMMARY OF THE INVENTION

This invention relates to Mn-Al-C alloy magnets which are superior tothose disclosed in U.S. Pat. No. 3,661,567.

Accordingly, it is an object of this invention to provide new highperformance anisotropic permanent magnets having high improved magneticcharacteristics. specimen heavy

It is another object of this invention to provide anisotropic MN-Al-Calloy magnets having magnetic characteristics such that the (BH)max isabove 4.8 × 10⁶ G.Oe and which reaches 9.2 × 10⁶ G.Oe in the bulk state.

It is another object of this invention to provide very excellentanisotropic permanent magnets which exhibit a specific gravity as low as5.1 and which have magnetic energies per unit weight comparable to thoseof the highest class of known permanent magnets, e.g., having energiesper unit weight 2˜3 times higher than those of anisotropic (Br,Sr)ferrite magnets, and 1.5˜2 times as high as AlNiCo magnets.

It is a further object of this invention to provide anisotropicpermanent magnets having excellent mechanical characteristics.

The present inventors have found that in Mn-Al-C alloy magnets, whichordinarily exhibit no plasticity, there exists a new, special phasegiving abnormally high plasticity in the specific temperature range of530°-830°C, in a compositional range wherein Mn is 68.0-73.0%, C(1/10Mn--6.6)% - (1/3 Mn--22.2)% and wherein the remainder is Al. Based onthese findings, the present inventors have successfully obtained Mn-Al-Calloy magnets which are anisotropic in their bulk state and which haveextraordinary and unexpected magnetic characteristics, through plasticdeformation of the alloy in the abnormally plastic range, while takingadvantage of the specific state of existence of the carbon component.

The striking improvement in magnetic characteristics achieved by way ofthe above-described plastic deformation is a new phenomenon based on thepeculiar mechanism which the Mn-Al-C alloy magnets possess. For example,in the case of Mn-Al alloy magnets, it was confirmed that the plasticityslightly appeared above 580°C, but that by the working above 530°C, noimprovement in magnetic characteristics was recognized at all; rather,the magnetic characteristics were greatly degraded.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a graph relating the particle diameter of the crystalsand the amount of carbon in Mn-Al-C alloy castings consisting of 72.0%Mn, 0.1-2.5% C, and the remainder Al;

FIG. 2 represents a photograph of an optical microstructure of the ε_(c)(M) phase;

FIG. 3 depicts a graph relating the pressuring time and the degree ofdeformation in the pressuring direction when the monocrystal in ε_(c)(M) was subjected to plastic deformation;

FIG. 4 exhibits diagrams showing the process of change in the crystalstructure undergoing the transformation: ε_(c) →ε_(c) '→τ_(c) ;

FIG. 5 displays a photograph of an optical microstructure of the τ_(c)(M) phase;

FIG. 6 is a graph relating to the degree of saturation deformation tothe pressuring direction;

FIG. 7 depicts the relationship between the amount of Mn and the degreeof anisotropization; and

FIG. 8 represents a composition diagram of a Mn-Al-C ternary system.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present inventors have studied and analyzed the reasons why themagnetic characteristics of Mn-Al-C alloy magnets were improvedespecially when the manufacturing conditions were restricted asdescribed in U.S. Pat. No. 3,661,567. As a result, it has been clarifiedthat this improvement was due to the particular state of existence ofcarbon in the Mn-Al-C alloy magnets, i.e., the manufacturing conditions,and their magnetic characteristics have an intimate relationship.Accordingly, under manufacturing conditions which make the state ofexistence of carbon inadequate, magnets having low magneticcharacteristics can be produced which are in the same order as isotropicMn-Al alloy magnets, even if the composition ratio of Mn, Al and C fallswithin the above mentioned ranges, and even wherein sufficient τ phaseexists.

It was discovered that in order to obtain isotropic permanent magnetsfrom Mn-Al-C alloys having excellent magnetic characteristics, it isnecessary that the phases existing in these alloys should mainlyinclude:

1. a magnetic phase having carbon forcibly melted therein beyond thesolubility limit, and

2. a phase of Mn₃ AlC and/or a face-centered cubic phase being similarto Mn₃ AlC in which the remaining excess carbon is separated out by wayof tempering in the form of carbides other than alumminum carbide (Al₄C₃, etc.) in fine grainy or reticular shape, and that phase (2) isseparated and dispersed finely in grainy or reticular form within phase(1) as its matrix. It has been proven than when alloys are producedaccording to the above-described phase conditions, magnets havinggreatly improved magnetic characteristics can be manufactured, whichalloys possess a stabilized magnetic phase. This state of existence ofcarbon, as described above, was confirmed by way of X-ray diffractiontechniques, optical microscopy and electron microscopy.

Mn₃ AlC is a compound having a face-centered cubic crystal structure ofa perovskite type (lattice constant a = 3.87A), but because its Curiepoint is 15°C, and it is nonmagnetic at room temperature, Mn₃ AlCitself, even when existing in the Mn-Al-C alloys, does not contribute tothe intensity of magnetization of the Mn-Al-C alloy magnets.

A face-centered cubic phase similar to Mn₃ AlC means that perovskitetype carbides appear in the Mn-Al-C alloys containing an amount ofcarbon more than the solubility limit, or precipitation substance havingchemical characteristics as that of said carbides but not formed carbideperfectly.

Al₄ C₃ is a carbide existing in the Mn-Al-C alloys containing Mn withinthe range of 68.0-73.0% and an amount of carbon in excess of (1/3 Mn --22.2)%. It is formed at temperatures above the melting points of Mn-Al-Calloys, but is neither formed nor destroyed by heat treatment in thetemperature range below the melting points. Al₄ C₃, hydrolyzed bymoisture in the air, etc., causes the alloys to crack, leading finallyto the decay of alloys with the further proceeding of hydrolysis.

It has been clarified that in Mn-Al-C alloys, the solubility limit ofcarbon in the magnetic phase, as determined by the measurement oflattice constants by way of X-ray diffraction and by measurement ofCurie point by use of a magnetic balance, is 0.6% for the composition of72% Mn, 0.4% for the composition of 70% Mn, 0.2% for the composition of68.0% Mn, and the solubility limit of carbon within the compositionrange of 68.0-73.0% Mn can be represented by the mathematical formula of(1/10 Mn--6.6)%.

On the other hand, the solubility limit of carbon in the hightemperature phase is almost the same as the solubility limit of carbonin the magnetic phase at a temperature of 830°C, but in a temperaturerange of 900°-1200°C, the solubility limit of carbon in this phase ismore than (1/10 Mn--6.6)% of carbon; however, by overcooling byquenching at a temperature above 900°C, and ε phase can be obtained inwhich more than (1/10 Mn--6.6)% of carbon is forcibly dissolved.

The high temperature phase into which carbon is forcibly dissolved inamounts beyond the solubility limit (1/10 Mn--6.6)% in Mn-Al-C alloys isdesignated the ε_(c) phase, to distinguish it from the ε phase of thehigh temperature phase containing carbon in amounts within thesolubility limit. Also, the ferro-magnetic phase in which carbon isforcibly dissolved in amounts beyond the solubility limit is designatedthe τ_(c) phase, to distinguish it from the τ phase of the magneticphase containing carbon in amounts within the solubility limit. Bysubjecting the alloys of this ε_(c) phase to the tempering as describedabove, the phase structure in which the phase of Mn₃ AlC and/or that ofa face-centered cubic phase being similar thereto, is finely dispersedin grainy or reticular form in these alloys, with the τ_(c) phaseforming the matrix. When, however, in the process of quenching, agradual cooling is made at a cooling rate lower than 10°C/min. in thetemperature range of 830°-900°C, and then, the quenching is carried outfrom this temperature, or when the alloys are held in the temperaturerange of 830°- 900°C for more than 7 minutes, preferably more than 10minutes, and quenching is from that temperature, Mn₃ AlC aligned inlamellae parallel to the special crystal plane of ε_(c) (0001) andkeeping intervals of 1-10μ is deposited in the ε_(c) phase. It has beenclarified by way of optical microscopic observation and X-raydiffraction that this lamellar Mn₃ AlC has a crystalline orientationrelationship of

    ε.sub.c (0001) // Mn.sub.3 AlC (111)

furthermore, as the ε_(c) phase in the space of 1-10μ, interposedbetween the lamellae of Mn₃ AlC, was closely observed under an electronmicroscope, it was confirmed under the electron microscope, but notdistinctly under the optical microscope, that the phase of Mn₃ AlCand/or face-centered cubic phase similar thereto were deposited on theplane of ε_(c) (0001), distanced from each other by 0.1-1μ.

The heat treatment whereby the phase of Mn₃ AlC and/or face-centeredcubic phase similar thereto was deposited in lamellae as describedabove, i.e., the heat treatment in which the allows are cooled at acooling rate lower than 10°C./min. in the temperature range of830°-900°C, or held in the temperature range of 830°-900°C for more than7 minutes, is specifically designated the M treatment, and the ε_(c)phase containing the lamellar phase of Mn₃ AlC and/or face-centeredcubic phase similar thereto deposited by the M treatment is abbreviatedat the ε_(c) (M) phase.

By tempering the alloys of the ε_(c) (M) phase, the matrix ε_(c)transforms into the τ_(c) phase, but the lamellar phase of Mn₃ AlCand/or face-centered cubic phase similar thereto remains as it is, andthen, the phase of Mn₃ AlC finely dispersed in grain form as mentionedabove or in a reticular phase of Mn₃ AlC and/or face-centered cubicphase similar thereto is barely recognizable.

The τ_(c) phase containing the lamellar phase of Mn₃ AlC and/orface-centered cubic phase similar thereto is abbreviated as the τ_(c)(M) phase. The isotropic Mn-Al-C alloy magnet including the τ_(c) (M)phase as isotropic matrix has a low level of magnetic characteristics inthe same order as the magnetic characteristics of isotropic Mn-Alalloys. The magnetic characteristics of Mn-Al-C alloy magnets is relatedto the existing condition of carbon, as mentioned above. Similarly, themagnetic characteristics and workability of anisotropic Mn-Al-C alloymagnets rendered anisotropic by warm plastic deformation, according tothis invention, are related to the existing condition of carbon.

Other and further objects, features and advantages of the invention willappear more fully from the following detailed description and Examples:

EXAMPLE 1

A monocrystal consisting of the ε_(c) phase of an Mn-Al-C allow having acomposition of Mn 72.28%, Al 26.64% and C 1.08%, as chemically analyzed,was manufactured.

As a result of studies on the various factors involved in obtaining theε_(c) monocrystal of this Mn-Al-C alloy, it was clarified that thegrowth of crystal necessary for monocrystallization is dependent onamounts of carbon.

It is, thus, an indispensable condition for obtaining the ε_(c)monocrystal that the amount of carbon falls within the range of (1/10Mn-6.6)% - (1/3 Mn-22.2)% (provided that, Mn 68.0-73.0%), and that theprocess of heating above 1,380°C and up to 1,500°C (the required meltingtemperature to forcibly melt carbon into its solid solution) be run atleast for one cycle. It was found out, for example, that whereas in theε phase in which the amount of carbon in its solid solution was lessthan (1/10 Mn-6.6)%. the growth of crystals in the alloy took place withdifficulty. However, in Mn-Al-C alloys in which carbon in an amount inexcess of the solubility limit of (1/10 Mn-6.6)% was forcibly meltedwell into its solid solution at a melting temperature of above 1,380°C,the coarsing of the crystal grains was notable. Accordingly, the ε_(c)monocrystal may be easily obtained by way of cooling the molten metal ofthis alloy from one end thereof by the Bridgman method or the chill moldmethod.

With regard to the growth of crystals of the ε_(c) phase, for example,in the case of polycrystals formed under the ordinary casting condition,as shown in FIG. 1, containing carbon in amounts above the solubilitylimit, the coarsening of the crystal grains becomes notable, and thegrain size of crystals increases with the increasing amount of forciblydissolved carbon; but as the amount of carbon exceeds (1/3 Mn-22.2)%,the excess carbon forms aluminum carbide Al₄ C₃, which is undesirable.For these reasons, the required amounts of carbon to obtain ε_(c)monocrystals are limited within the range of (1/10 Mn--6.6)%-(ΔMn--22.2)% as mentioned above.

In order to forcibly melt the carbon well into solid solution, it mustbe heated to a temperature of higher than 1,380°C. At meltingtemperatures lower than 1,380°C, it is not possible to forcibly dissolvecarbon into its solid solution in amounts beyond the solubility limit.

Accordingly, in the case of obtaining the ε_(c) monocrystals, therespective component elements were mixed and alloyed by heating themabove 1,380°C, and then, monocrystallized. On the other hand, a Mn-Al-Calloy in which carbon was preliminarily dissolved into its solidsolution at a temperature above 1,380°C, was remelted andmonocrystallized. In the latter instance, the heating temperature forthe ε_(c) monocrystallization was not necessarily required to be above1,380°C, since heating at a temperature above its melting point of1,210°-1,250°C was sufficient.

The temperature control conditions for obtaining the ε_(c) monocrystalby cooling the molten metal of the Mn-Al-C alloy from one end werechosen as follows:

The molten metal was solidified at a falling rate of 0.5-10 cm/hr undera temperature gradient of 5°-200°C/cm in a temperature range of1,150°-1,250°C, or solidified from one end at a cooling rate of10°-100°C/hr in the aforementioned temperature range, and themonocrystal was, then, cooled to 900°C, and thereafter, quenched from atemperature of 900°C to a temperature below 500°C by cooling it in thetemperature range of 900°-500°C at a cooling rate of 300°-3,000°C/min.In this way, a ε_(c) monocrystal in the shape of a cylinder of 35 mmoutside diameter could be easily obtained.

From the ε_(c) monocrystal obtained in this way, a cubic test piece of 8× 8 × 8 mm having surfaces of (0001), (1100) and (1120) was cut out.This ε_(c) monocrystal was tempered at 600°C for 1 hour. The temperedtest piece was found to be magnetically isotropic, as its magneticcharacteristics were measured. The magnetic characterstics found were:

    Br = 2,750 G, .sub.B HC = 1,350 Oe, and (BH)max = 1.1 × 10.sup.6 G.Oe, which were equivalent to the magnetic characteristics of isotropic Mn-Al-C alloy magnets of the ordinary polycrystal type. By optical microscope observation of the structure of the test piece after being tempered, a finely dispersed grainy or reticular deposition of the Mn.sub.3 AlC phase was observed, just as in the structure of the ordinary isotropic magnet. From the result of the X-ray diffraction, however, it was confirmed that since the intensity of diffracted lines from the Mn.sub.3 AlC phase differed, depending on the diffracting surfaces of the test piece. a small amount of the Mn.sub.3 AlC phase oriented in its relationship to the ε.sub.c phase before being tempered as expressed by ε.sub.c (0001) // Mn.sub.3 AlC (111) existed.

Furthermore, other test pieces subjected to similar experiments asdescribed above, with other surfaces cut out and the temperingconditions altered, were all found to be isotropic magnets, in which noimprovements in their magnetic characteristics were recognized.

EXAMPLE 2

An ε_(c) monocrystal obtained in Example 1, was subjected to the Mtreatment in which it was held at a temperature of 830°C for 20 minutes,and was then quenched from this temperture at a cooling rate of300°-3,000°C/min. The monocrystal thus-obtained had the phase (expressedε_(c) (M) monocrystal) in which the Mn₃ AlC phase was orderly depositedin the shape of a lamellae on the (0001) plane of the ε_(c) monocrystal,as described hereinbefore. The orientation relationship was found to be:

    ε.sub.c (0001) // Mn.sub.3 AlC (111)

as described above, which was confirmed by way of X-ray diffraction,X-ray microanalysis, optical microscopy and chemical analysis.

FIG. 2 presents a photograph of optical microstructure (magnification:1,000 ) showing a state in which the Mn₃ AlC phase is deposited in theshape of a lamellae in the matrix of ε_(c).

After deciding the crystal orientation by utilizing the lamellarstructure and X-ray diffraction, from the ε_(c) (M) monocrystal obtainedas described above, a cubic test piece of 8 × 8 × 8 mm having surfacesof (0001), (1100) and (1120) was cut out, and was subjected to atempering at 570°C for 1 hour to obtain the τ_(c) (M) phase. It wasrecognized by way of optical microscopic observation and X-raydiffraction that the ε_(c) phase of the matrix was transformed into theτ_(c) phase by this tempering, but the lamellar structure was notdestroyed.

The magnetic characteristics of the test piece of the τ_(c) (M) phasewere quite isotropic. They were found to be:

    Br = 2,500 G, .sub.B Hc = 800 Oe, and (BH)max = 0.67 × 10.sup.6 G.Oe,

which were lower than the magnetic characteristics of the ordinaryisotropic Mn-Al-C alloy magnets of the polycrystal type. Other testpieces observed, with the face cut out and the treating condition widelyaltered, were all found to be isotropic, and no improvement in magneticcharacteristics was recognized in these test piece.

EXAMPLE 3

A monocrystal in the ε_(c) (M) phase of an Mn-Al-C alloy containing72.10% Mn, 26.78% Al and 1.12% C, as chemically analyzed, wasmanufactured in the manner similar to that of Example 2, and from thismonocrystal in the ε_(c) (M) phase, several cubic test pieces were cutout, each of 10 × 10 × 10 mm, having 3 surfaces respectively beingparallel to the 3 crystal planes of (3304), (1120) and (3308). When oneof the test pieces was subjected to pressure at a temperature of 550°Cand at a pressure of 30 kg/mm² in the direction perpendicular to the(3304) plane, using a oil-hydraulic press machine to deform itplastically in the ε_(c) (M) phase, it was found that a rapid shrinkagein the pressuring direction took place within several minutes (B point)after the pressuring was begun (A point), leading to a rapid and notableplastic deformation. (See the deformation curve of FIG. 3.) This rapidshrinkage in the pressuring direction reached a saturation (C point) ata degree of shrinkage of 15%, as expressed by the ratio of the length ofthe test piece before and the length of the test piece after pressuring,and barely underwent a change (D point), even though the pressuring timewas extended beyond that point. The magnetic characteristics of thistest piece after being subjected to a warm deforming operation weremeasured to be low, but by subjecting this test piece to tempering at atemperature of 570°C, an anisotropic magnet having very excellentmagnetic characteristics oriented in one direction with its preferreddirection of magnetization at about right angles to the pressuringdirection was obtained.

For the purpose of making detailed studies of the phenomenon that arapid and notable plastic deformation is induced by warm deformation ofthe ε_(c) (M) phase and of the phenomenon that, by tempering after thisdeformation, anisotropic magnets oriented in one direction are obtained,similar experiments as that above described were pursued, with thedegree of deformation diversified as described below, to examine thephase of the test piece in deformation process.

First, the test piece deformed by pressuring to B point just before therapid plastic deformation begins is designated as S₁, the test piecedeformed by pressuring to E point intermediary between B point and Cpoint as S₂, the test piece deformed by pressuring just before C pointwhere the rapid plastic deformation ends as S₃, and the test piecedeformed by pressuring to D point mentioned above as S₄, respectively.The degrees of deformation in these test pieces were found to be: S₁--1.9%, S₂ --7.3%, S₃ --14.6% and S₄ --15.0%. With regard to the shapeof the test pieces after being subjected to this warm deformation, thedegrees of elongation were different in the directions of measurement inevery test piece, particularly, in the test pieces of S₃ and S₄,elongations in the direction corresponding to the directionperpendicular to (3308) before their pressuring were notable, but onlysmall elongations were recognized in the direction corresponding to thedirection perpendicular to (1120) before their pressuring.

As the phase of these 4 test pieces after being deformed was examined byway of X-ray diffraction, with the test pieces of S₁, S₂ and S₃, a quitenew diffraction pattern which has never been observed before from eitherthe Mn-Al alloys or the Mn-Al-C alloys was found. This quite newdiffraction pattern, as a result of its analysis, was found to be due tothe existence of a new phase of orthorhombic structure with latticeconstants of a = 4.371A, b = 2.758A and c = 4.582A, which crystalstructure belongs to B19 type (MgCd type) in terms of theStruktur-Bericht type expression, thus making evident the existence ofquite a new phase differing from the usual phases ε, ε_(c), τ, τ_(c), orsuch carbides as Mn₃ AlC. It was also clarified that this orthorhombiccrystal phase is an order phase which makes its appearance at theintermediary stage in the ε_(c) → τ_(c) transformation process, and theε → ε_(c) ' transformation is an order-disorder transformation, whereε_(c) ' designates the order phase of this orthorhombic crystal.

In Table 1, the results of the X-ray diffraction of the ε_(c) ' phase bythe powder method are shown. With the test piece of S₁, only thediffracted lines from the aforementioned new ε_(c) ' phase were found,except for the diffracted lines due to the lamellar Mn₃ AlC phase, andmoreover, it became apparent that the ε_(c) ' phase is a crystaloriented in one direction, and that between the ε_(c) phase of thematrix before the pressuring and the ε_(c) ' phase of the matrix afterthe pressuring, there exists crystal orientation relationships of

    ε.sub.c (0001) // ε.sub.c '(100), ε.sub.c [0001] // ε.sub.c '[100]

                  Table 1                                                         ______________________________________                                        Observed                Calculated                                            values                  values                                                Interfacial                                                                            Relative  Miller   Interfacial                                                                            Relative                                 distance (A)                                                                           intensity indices  distance (A)                                                                           intensity                                ______________________________________                                        4.587    5         001      4.582    7.4                                      3.162    8         101      3.163    17.3                                     2.764    3         010      2.758    7.0                                      2.363    14        011      2.363    24.9                                     2.292    16        002      2.291    12.4                                     2.186    44        200      2.186    41.0                                     2.077    100       111      2.079    100.0                                    2.033    38        102      2.029    49.9                                                        201      1.973    1.3                                                         012      1.762    0.8                                      1.712    3         210      1.713    11.4                                                        112      1.643    3.8                                      1.606    13        211      1.604    14.1                                     1.586    6         202      1.581    7.1                                                         003      1.527    1.0                                                         301      1.388    1.1                                      1.381    6         020      1.379    8.7                                                         212      1.372    0.7                                      1.338    11        013      1.336    17.3                                                        021      1.320    0.3                                                         121      1.264    1.6                                                         203      1.252    1.2                                      1.240    16        311      1.240    22.9                                     1.228    6         302      1.229    11.4                                                        022      1.181    3.7                                      1.167    16        220      1.166    15.1                                                        004      1.146    1.9                                       1.1411  24        122      1.141    23.2                                                        213      1.140    30.2                                     ______________________________________                                    

With the test piece of S₂, the diffracted lines from the ε_(c) ' phaseand the diffracted lines from the τ_(c) phase existed, besides thediffracted lines from the lamellar Mn₃ AlC phase, and moreover, theε_(c) ' phase and the τ_(c) phase were both oriented to one direction.With the test piece of S₃, the diffracted lines from a small amount ofε_(c) ' phase and a large amount of τ_(c) phase existed, besides thediffracted lines from the lamellar Mn₃ AlC phase, and moreover, theε_(c) ' phase and τ_(c) phase were both unidirectionally oriented as inthe case of S₂. Between the unidirectionally oriented ε_(c) ' phase andτ_(c) phase, there existed such a specific crystal orientationrelationship as:

    ε.sub.c ' (100) // τ.sub.c (111).

With the test piece of S₄, only the diffracted lines from the τ_(c)phase were found, other than the diffracted lines from the lamellar Mn₃AlC phase, and moreover, the τ_(c) phase was found nearlyunidirectionally oriented.

The angle of the diffracted lines from the τ_(c) phase in the testpieces of S₂, S₃ and S₄ were a little deviated from the angles of thediffracted lines from the ordinary τ_(c) phase in the isotropic Mn-Al-Calloy magnets, and thus, some difference in lattice constants wasobserved.

As these test pieces after being deformed were subjected to a tempering(tempering temperature 580°C) without pressing, the magneticcharacteristics of the test pieces after being tempered improved withthe increasing tempering time; very excellent anisotropic magnets havingrespectively their magnetic characteristics shown in Table 2 wereobtained in the tempering time of 18 hours with S₁, 24 hours with S₂, 30hours with S₃ and 15 hours with S₄.

It is to note that the right angle direction (1) in Table 2 denotes themeasuring direction at a right angle to the pressuring direction andcorresponding to the direction perpendicular to the (1120) plane beforethe pressuring, and the right angle direction (2) the measuringdirection at a right angle to the pressuring direction but correspondingto the direction perpendicular to the (3308) plane before thepressuring.

                                      Table 2                                     __________________________________________________________________________                         After the deforming                                                                             After the tempering                    Name of                                                                             Measuring direction                                                                          Br   B.sup.Hc                                                                           BHmax   Br   B.sup.Hc                                                                           BHmax                        test piece           (G)  (Oe) (× 10.sup.6 G.Oe)                                                               (G)  (Oe) (× 10.sup.6            __________________________________________________________________________                                                     G.Oe)                              Pressuring direction             1,100                                                                              450  0.3                          S.sub.1                                                                             Right angle direction (1)                                                                    Nonmagnetic       ≈ 0                                                                        ≈ 0                                                                        ≈ 0                        Right angle direction (2)        6,650                                                                              1,950                                                                              6.5                                Pressuring direction                                                                         ≈ 0                                                                        ≈ 0                                                                        ≈ 0                                                                           750  300  0.1                          S.sub.2                                                                             Right angle direction (1)                                                                    ≈ 0                                                                        ≈ 0                                                                        ≈ 0                                                                           ≈ 0                                                                        ≈ 0                                                                        ≈ 0                        Right angle direction (2)                                                                    200  100  <0.1    6,850                                                                              2,150                                                                              7.2                                Pressuring direction                                                                         ≈ 0                                                                        ≈ 0                                                                        ≈ 0                                                                           ≈ 0                                                                        ≈ 0                                                                        ≈ 0                  S.sub.3                                                                             Right angle direction (1)                                                                    ≈ 0                                                                        ≈ 0                                                                        ≈ 0                                                                           ≈ 0                                                                        ≈ 0                                                                        ≈ 0                        Right angle direction (2)                                                                    550  200  0.1     6,900                                                                              2,300                                                                              9.1                                Pressuring direction                                                                         950  500  0.2     1,400                                                                              600  0.3                          S.sub.4                                                                             Right angle direction (1)                                                                    200  100  <0.1    500  200  <0.1                               Right angle direction (2)                                                                    4,300                                                                              1,650                                                                              1.3     6,700                                                                              2,250                                                                              6.8                          __________________________________________________________________________

Of these test pieces, that of S₃ after being tempered was found, as aresult of observation by X-ray diffraction, to be a τ_(c) (M)monocrystal with its C axis, the easy axis of magnetization of the τ_(c)phase of the matrix, oriented in the direction making an angle of about82° to the pressuring direction. As this test piece was cut out, and itsmagnetic characteristics in the easy direction of magnetization (C axisdirection) were measured, they were found to be very excellent:Br =7,000 G B.sup. HC = 2,300 Oe BHmax = 9.2 × 10⁶ G.Oe4πI₁₀₀₀₀ = 7,100 GI.sup. HC = 2,350 Oe Br/4πI₁₀₀₀₀ = 0.98

When a disc test piece containing the easy direction of magnetization inthe direction parallel to the disc surface was cut out of thismonocrystal test piece, and its magnetic torque was measured, its value(it corresponds to an anisotropy constant) was found to be 1.07 × 10⁷dyne-cm/cm³. Furthermore, the magnetic torque was measured likewise ofthe test pieces of S₁, S₂ and S₄ after being tempered. The values wererespectively, 0.93 × 10⁷ dyne-cm/cm³, 0.97 × 10⁷ dyne-cm/cm³ and 0.95 ×10⁷ dyne-cm/cm³, and as the degree of anisotropization was expressed bytheir ratio to the value of magnetic torque of monocrystal, i.e., the1.07 × 10⁷ dyne-cm/cm³ above mentioned, all of these test pieces hadsuch very high degrees of anisotropization, e.g. more than 0.9.

The crystal direction of the τ_(c) phase after being tempered was thesame as the crystal direction of the τ_(c) phase before being tempered,and the change in the crystal direction of the τ_(c) phase due to thetempering was barely recognized.

Furthermore, as a result of making detailed studies of the phenomenon ofrapid plastic deformation in the warm deforming of the ε_(c) (M) phaseabove described and of the process of forming the unidirectionallyoriented anisotropic magnets, it became evident that these phenomena arebased on the ε_(c) → ε_(c) '→ τ_(c) transformation made in specificcrystal orientation relationships.

Thus, when a monocrystal in the ε_(c) (M) phase is pressured in thedirection above mentioned, the matrix turns into a monocrystal in ε_(c)' having the crystal orientation relationships of

    ε.sub.c (0001) // ε.sub.c ' (100)

    ε.sub.c [0001] // ε.sub.c ' [100]

through an order-disorder transformation of ε_(c) → ε_(c) '. This ε_(c)→ ε_(c) ' transformation corresponds to the process followed from Apoint to B point in FIG. 3, and the shrinkage in the pressuringdirection is not excessively large.

Furthermore, the ε_(c) ' monocrystal transforms into a τ_(c) monocrystalhaving the relationship of ε_(c) ' (100) // τ_(c) (111) through theε_(c) '→ τ_(c) martensitic transformation in which the specific (100)plane slides to the direction of [001] at a specific distance.

The sliding of the plane to the specific direction rapidly takes placein avalance-like manner, and induces a rapid shrinkage in the pressuringdirection from point B to point C. Then, at the point of time when thesliding of all of the plane in the monocrystal has finished, that is tosay, all parts of ε_(c) ' transformed into τ_(c), i.e., at point C, theshrinkage in the pressuring direction stops. After all parts of ε_(c) 'had been transformed into τ_(c), little deformation occurred, even whenthe pressuring was continued.

FIG. 4 presents diagrams showing the changing process of the crystalstructure in the ε_(c) → ε_(c) '→ τ_(c) transformation described above.FIG. 4-(1) represents a diagram showing the crystal structure of thephase of ε_(c), (2) that of ε_(c) ', and (3) that of τ_(c). The diagramof (1) portrays a view of the ε_(c) phase taken from the directionsperpendicular respectively to its (0001) plane and (1120) plane; (2),that of ε_(c) ' seen perpendicular to its (100) plane and (010) plane;and (3), that of τ_(c) seen perpendicular to its (111) plane and (110)plane. The solid lines designate respective crystal lattices; the dottedlines, the locational relationship of atoms; and the arrows, the movingdirection of the plane of atoms. The double circles indicate thepositions of atoms of Mn or Al in the disorder structure; the blankcircle and the solid circle respectively show the positions of atoms ofAl and Mn in the order structure. The positions of atoms of carbon beingin the state of solid solution were omitted.

The τ_(c) after being deformed has very low magnetic characteristics,but it turns into an anisotropic magnet having very excellent magneticcharacteristics when tempered.

It became apparent that based on such a mechanism, the phenomenon ofrapid plastic deformation takes place, and the unidirectionally orientedanisotropic magnet is formed. Accordingly, the optical microstructure ofthe test piece after being subjected to the warm deforming was found tobe quite uniform and smooth, although the existence of the lamellar Mn₃AlC phase was observed, as shown by the structure photograph at amultiplicity of 1,000 in FIG. 5, and the fragmented or broken structureof crystal due to slip lines or twin structure which were observed inthe structure of ordinary alloys after being deformed were not observed.

It became evident that the rapid plastic deformation in the warmdeformation of the ε_(c) (M) phase is not the deformation due to slip ortwin which is observed in the ordinary plastic deforming of other metalsor alloys, but the deformation based on the ε_(c) ' → τ.sub. martensitictransformation. Accordingly, the saturation of this deformation is basedon a mechanism entirely different from that of the saturation of theordinary deformation due to the hardening by the working of metals oralloys. Furthermore, it was made clear that the anisotropy of elongationin the test piece after being worked mentioned above is due to thesliding of the specific plane to a specific direction in the ε_(c) '→τ_(c) transformation.

In the test piece of S₁ and S₂, shrinkages in the direction of formerpressuring were recognized after making the tempering, and S₁ was foundto have shrunk by 5.5%, and S₂ by 6.0% after making the tempering ascompared to before making the tempering. A likely interpretation of thisphenomenon is: from ε_(c) ' crystal which is formed by transformingunder pressure, directionally oriented τ_(c) crystal seems to have beenformed even by the ε_(c) ' → τ_(c) transformation without pressure. Inorder to obtain unidirectionally oriented magnets having the mostexcellent magnetic characteristics, however, it is essential to proceedwith the warm deforming just before reaching the saturation deformation,i.e., just before C point in FIG. 3.

EXAMPLE 4

An experiment of plastic warm deforming similar to that of Example 3 wasperformed by changing the pressuring direction, pressuring temperatureand pressuring force.

A monocrystal in the ε_(c) (M) phase of an Mn-Al-C alloy having thecomposition of Mn 71.93%, Al 27.02% and C 1.05%, as chemically analyzed,was manufactured by the similar method as that of Example 2, and fromthis monocrystal in the ε_(c) (M) phase, a cubic or rectangularmonocrystal test piece to be pressured having sides of 5-12 mm were cutout. The test piece to be pressured were so cut out as to have 3 faces(a), (b) and (c) making a right angle to each other:

a. a face perpendicular to the pressuring direction,

b. a face parallel to the crystal face containing the pressuringdirection and the ε_(c) [0001] direction, and

c. a face making right angles to (a) and (b).

The cut out test pieces were deformed by applying a pressure of 10-40kg/mm² on a oil-hydraulic press at a temperature range of 500°-850°C,and were then, further subjected to a tempering in the temperature rangeof 550°-650°C. The preferred direction of magnetization of the testpieces after being tempered was determined by way of X-ray diffractionor measurement of magnetic torque or measurement of the magnetizationcurves in varied directions, and its magnetic characteristics in thepreferred direction of magnetization were measured.

Table 3 shows the conditions of warm deformation (pressuring direction,pressuring temperature, degree of deformation in the pressuringdirection) of each test piece and the values of its magneticcharacteristics in the preferred direction of magnetization aftertempering. The pressuring direction was further distinguished byexpressing it by the angles of θ₁ and θ₂, assuming the angle made by thepressuring direction and the ε_(c) [0001] direction as θ₁ and the anglemade by the projected axis of the pressuring direction on the ε_(c)(0001) face and the ε_(c) [1100] as θ₂. For example, the pressuringdirection of θ₁ = 90°, θ₂ = 0° is perpendicular to the ε_(c) (1100)plane and the pressuring direction perpendicular to the (3304) plane ofExample 3 is expressed approximately by θ₁ = 55°, θ₂ = 0°.

                                      Table 3                                     __________________________________________________________________________    Designation                                                                           Pressuring     Degree of                                              of test piece                                                                         direction                                                                             Temperature                                                                          deformation                                                                          Br   B.sup.Hc                                                                           (BH)max                                       θ.sub.1                                                                     θ.sub.2                                                                     (°C)                                                                          (%)    (G)  (Oe) (× 10.sup.6 G.Oe)               __________________________________________________________________________    S.sub.5 0°                                                                         0°                                                                         600    - 0.8  3,300                                                                              1,400                                                                              1.8                                   S.sub.6 20°                                                                        0°                                                                         550    - 2.6  4,750                                                                              1,550                                                                              3.3                                   S.sub.7 35°                                                                        0°                                                                         550    -12.0  6,500                                                                              2,050                                                                              7.2                                   S.sub.8 55°                                                                        0°                                                                         500    - 0.2  2,900                                                                              1,500                                                                              1.6                                   S.sub.9 55°                                                                        0°                                                                         530    -14.8  6,900                                                                              2,250                                                                              9.0                                   S.sub.10                                                                              55°                                                                        0°                                                                         720    -14.5  6,800                                                                              2,200                                                                              8.1                                   S.sub.11                                                                              55°                                                                        0°                                                                         850    -14.0  2,600                                                                              1,600                                                                              1.4                                   S.sub.12                                                                              55°                                                                        0°                                                                         650    - 0.4  2,950                                                                              1,400                                                                              1.1                                   S.sub.13                                                                              55°                                                                        0°                                                                         600    -25.0  3,100                                                                              1,800                                                                              2.0                                   S.sub.14                                                                              70°                                                                        0°                                                                         580    -12.0  6,600                                                                              2,000                                                                              7.3                                   S.sub.15                                                                              90°                                                                        0°                                                                         530    - 2.0  6,250                                                                              2,300                                                                              7.6                                   S.sub.16                                                                              90°                                                                        0°                                                                         560    - 3.2  6,100                                                                              2,150                                                                              7.0                                   S.sub.17                                                                              35°                                                                        10°                                                                        830    -12.9  6,400                                                                              2,100                                                                              7.0                                   S.sub.18                                                                              35°                                                                        15°                                                                        550    -11.7  6,350                                                                              2,050                                                                              6.6                                   S.sub.19                                                                              70°                                                                        15°                                                                        600    -10.0  6,400                                                                              1,750                                                                              6.2                                   S.sub.20                                                                              55°                                                                        20°                                                                        650    - 6.2  4,150                                                                              1,500                                                                              2.3                                   S.sub.21                                                                              50°                                                                        30°                                                                        580    - 4.4  3,700                                                                              1,350                                                                              2.2                                   S.sub.22                                                                              90°                                                                        30°                                                                        560    - 0.5  3,300                                                                              1,300                                                                              1.7                                   __________________________________________________________________________

Considering the symmetry of the hexagonal crystal, θ₁ and θ₂ wereassumed to fall within the angle ranges of 0° ≦ θ₁ ≦ 90°, 0° ≦ θ₂ ≦ 30°.All pressuring directions falling outside these angle ranges can bereplaced in terms of the pressuring directions falling within theaforementioned angle ranges, on the basis of the symmetry of thehexagonal crystal.

the results of the experiments conducted by altering the pressuringdirection were that most of the pressuring directions were effective inproducing anisotropic magnets, but large differences were recognized inthe values of the magnetic characteristics, depending on the pressuringdirection. Especially when the pressuring direction fell within theangle ranges of 35° ≦ θ₁ ≦ 90°, 0° ≦ θ₂ ≦ 15°, anisotropic magnetshaving very excellent magnetic characteristics with (BH)max in theirpreferred direction of magnetization above 6 × 10⁶ G.Oe were obtained.On the other hand, in the cases of the pressuring directions being θ₁ =0, θ₂ = 0, and θ₁ = 90°, θ₂ = 30°, the magnets obtained were nearlyisotropic, allowing only some predominance in magnetic characteristicsin the direction at a right angle to the pressuring direction. Thepreferred direction of magnetization where the maximum values ofmagnetic characteristics appear varies, depending on the pressuringdirection used. For example, when θ₁ = 55°, θ₂ = 0°, the test piece S₉showed such a direction making an angle of about 82° to the pressuringdirection, and when θ₁ = 70°, θ₂ = 0°, the test piece S₁₄ showed adirection making about 70° to the pressuring direction. All of themobtained were in the τ_(c) (M) phase unidirectionally oriented in whichthe τ_(c) [001] axis was abounding in the preferred direction ofmagnetization. In the test piece S₁₅, and when θ₁ = 90°, θ₂ = 0, thepreferred direction of magnetization lay in the pressuring direction,but the τ_(c) [001] axis did not lie in the pressuring direction. Butthe τ_(c) [001] axis was found in two directions making an angle ofabout 37° to the pressuring direction as the center of symmetry.

The magnetic characteristics of the τ_(c) (M) crystals which are formedfrom the ε_(c) (M) monocrystals by warm deformation and tempering dependon the degree of orientation of the τ_(c) (M) crystals. The orientationof the τ_(c) (M) crystals relates closely to the direction of pressure.And also, the orientation relates to the orientation of the ε_(c) '(M)phase before being transformed: thus when the pressuring direction fallswithin the angle ranges of 35°≦ θ₁ ≦ 90°, 0° ≦ θ₂ ≦ 15°, the ε_(c) 'phase of the matrix formed by the ε_(c) → ε_(c) ' transformation isnearly unidirectionally oriented, and then, the one-directional ortwo-directional τ_(c) phase was formed by the ensuing ε_(c) ' → τ_(c)transformation. On the other hand, it was made clear by the X-raydiffraction that when the pressuring directions are θ₁ = 0°, θ₂ = 0°,and θ₁ = 90°, θ₂ = 30° multi-directional ε_(c) ' (M) phase is formed,with resultant formation of the multi-directional τ_(c) (M) phase.

Accordingly, it was confirmed that it is essential to form a nearlyuni-directional ε_(c) ' (M) phase, in order to obtain anisotropicmagnets having magnetic characteristics of (BH)max above 6.0 × 10⁶ G.Oe.

When varying pressuring temperatures were used, in case of pressuringdirections falling within the angle ranges of 35° ≦ θ₁ ≦ 90°, 0° ≦ θ₂ ≦15° were used, within the temperature range of 530° - 830°, anisotropicmagnets having excellent magnetic characteristics of (BH)max above 6 ×10⁶ G.Oe were obtained, but below the temperature of 500°C,anisotropization did not occur with almost negligible plasticity, andabove the temperature of 850°C, the magnetic characteristics were nearlyisotropic, with lessened plasticity. Besides, deformation velocityincreases with a rising temperature rise up to 750°C.

As the relationship between the degree of deformation and the magneticcharacteristics was examined, the magnetic characteristics of the testpieces remained low, when the test pieces pressured in directionsfalling with the angle ranges of 35° ≦ θ₁ ≦ 90°, 0° ≦ θ₁ ≦ 15° shrunkbeyond the degree of saturation deformation described later, aspreviously described in Example 3, or when the degree of deformation didnot reach to one-tenth of the degree of saturation deformation.

The degree of saturation deformation is given by theoreticallycalculating, on the basis of the mechanism of transformation of Example3, the degree of deformation measured as it reaches the saturation inthe pressuring direction, when the ε_(c) (M) monocrystal turns into theτ_(c) (M) monocrystal by way of ε_(c) → ε_(c) ' → τ_(c) transformationdue to the slide of the plane of atoms in the specific directionmentioned in Example 3. Accordingly, the degree of saturationdeformation differs, depending on the pressuring direction. For example,the degree of saturation deformation obtained when θ₁ was changed, withθ₂ = 0°, are shown in FIG. 6. Test pieces deformed beyond the degrees oftheir saturation deformation showed isotropic elongation, were notdirectionally oriented in their magnetic characteristics, and were allascertained to consist of a multi-directionally oriented τ_(c) (M)phase, as examined by way of X-ray diffraction.

EXAMPLE 5

From the same ε_(c) (M) monocrystal as in Example 3, a cubic test pieceof 8 × 8 × 8 mm having faces of (0001), (1100) and (1120) was cut out,and then it was held at a temperature of 500°C for 5 minutes. The phasestructure of this test piece was examined by way of X-ray diffraction;as the result, it was recognized that the ε_(c) ' (M) phase occupies agreater part of the phase of the test piece.

This test piece was pressured and deformed at a temperature of 550°C, atpressure of of 35 kg/mm² in the direction perpendicular to (1100) planeand its magnetic characteristics were measured. The magneticcharacteristics found in the pressuring direction were;

    Br = 5300 G, .sub.B Hc = 2200 Oe, (BH)max = 4.1 × 10.sup.6 G.Oe

Then, this test piece was held further at a temperature of 600°C for 1hour, as the result, an anisotropic magnet was obtained, having magneticcharacteristics of:

    Br = 5700 G, .sub.B Hc = 2100 Oe, (BH)max = 5.2 × 10.sup.6 G.O3

thus, it was clarified that the anisotropic Mn-Al-C alloy magnet can beobtained by deforming the ε_(c) ' (M) phase.

EXAMPLE 6

A Mn-Al-C alloy having the unidirectional τ_(c) (M) phase manufacturedby the methods of Examples 3 and 4 was subjected to a warm plasticdeformation with the pressuring direction altered.

The test piece S₉ in the unidirectional τ_(c) (M) phase manufactured byway of a warm plastic deforming and tempering in Example 4 was pressuredagain by applying a pressure of 40 kg/mm² at a temperature of 600°C inthe same direction as that of the initial pressuring. In that operation,barely any deformation took place. Then, as the pressuring wascontinued, with the pressure further increased to 80 kg/mm², the testpiece shrunk by 8% in the pressuring direction, and isotropicallyelongated at a right angle to the pressuring direction. Measurement ofthe magnetic characteristics of the test piece after being pressuredshowed that the unidirectional orientation of the τ_(c) (M) phase aredisturbed, and the magnetic characteristic in the preferred direction ofmagnetization before making the pressuring greatly lowered the BHmax to3.8 × 10⁶ G.Oe.

As the test piece of S₃ consisting of the monocrystal in the τ_(c) (M)phase after being tempered in Example 3 was pressurized again byapplying a pressure of 40 kg/mm² at a temperature of 600°C in thedirection parallel to the direction of easy magnetization which wasnearly at a right angle to the initial pressuring direction, a rapidplastic deformation reaching the similar saturation as that of FIG. 3was observed. The degree of shrinkage in the pressuring directionreached -27%, while the elongation in the direction at a right angle tothe pressuring direction was as large as 28% in the direction parallelto the initial pressuring direction, and only about 1% elongation wasrecognized in another right angle direction; thus a directionaldifference in elongation was evident. As the magnetic characteristics ofthis test piece were measured, the preferred direction of magnetizationgreatly shifted toward the direction in which a notable elongation tookplace, that is, the direction nearly parallel to the initial pressuringdirection, and accordingly, the magnetic characteristics in thepreferred direction of magnetization observed before making thepressuring, that is, the pressuring direction, were distinctly lowered.

The phenomena of the notable plastic deformation taking place as themonocrystalline test piece in the τ_(c) (M) phase is pressured in thepreferred direction of magnetization, and of the preferred direction ofmagnetization greatly shifting, as noted by the examination of X-raydiffraction and electron-microscopic observations, were clarified to bebased on the reversibility of the ε_(c) ' ⃡ τ_(c) transformationinvolving the slide of the plane of atoms in just the opposite directionto that specific direction in which the slide of the plane of atomsoccurs in the previously described ε_(c) ' → τ_(c) transformation.

As the monocrystal in the τ_(c) (M) phase formed by the ε_(c) ' → τ_(c)transformation of Example 3 is pressured in the preferred direction ofmagnetization, that is, in the direction of τ_(c) [001], the surface ofatoms parallel to the τ_(c) (111) plane which holds the relationship ofε_(c) ' (100) // τ_(c) (111), slides by a specific distance, receivingthe stress in the direction of τ_(c) [112]. This transfer of the planeof atoms is a slide just in opposite direction to that of the transferin the ε_(c) ' [001] direction in the plane of atoms parallel to theε_(c) ' (100) plane in the ε_(c) ' → τ_(c) transformation whichcorresponds to the τ_(c) → ε_(c) ' transformation. Furthermore, from theε_(c) ' phase formed by the τ_(c) → ε_(c) ' transformation, by slidingat a specific distance in the direction of the ε_(c) ' [001] in theplane of atoms parallel to the ε_(c) ' (100) plane, a new unidirectionalτ_(c) phase which is different in crystalline azimuth from the τ_(c)phase before making the pressuring is formed. Such a slide of the planeof atoms parallel to the τ_(c) (111) plane was recognized only on theplane of atoms parallel to the τ_(c) (111) plane which holds therelationship of ε_(c) ' (100) 11 τ_(c) (111), but the surface of atomsparallel to a group group of other τ_(c) (111) planes differing in thesurface direction evidenced no slide. The structure after making thepressuring, as examined on an optical microscope, was found to be auniform smooth structure except for the lamellar Mn₃ AlC phase, just asdescribed in Example 3, and such structures as that having slip linesand the like were not observed. The magnetic characteristics of thenewly formed τ_(c) (M) phase in the preferred direction of magnetizationwere found to be:

    Br = 6,850 G .sub.B Hc = 1,900 G (BH)max = 7.0 × 10.sup.6 G.Oe

As the test piece of S₁₅ of Example 4 having two different τ_(c) [001]axes was pressured by applying a pressure of 35 kg/mm² at a temperatureof 600°C in the direction parallel to one τ_(c) [001] axis, a rapidplastic deformation reaching the similar saturation as that of FIG. 3was observed, and a directional difference in elongation was recognized.As the test piece which has been pressured was examined by way of X-raydiffraction, it was confirmed that this test piece was in aunidirectional τ_(c) (M) phase, that the direction of its τ_(c) [001]axis was parallel to the direction of one τ_(c) [001] axis observedbefore making the pressuring which differed from the pressuringdirection and that one τ_(c) [001] axis was shifted to the other τ_(c)[001] axis by the pressuring. This shifting of τ_(c) [001] axis wasdetermined to be based on the reversibility of the ε_(c) ' ⃡ τ_(c)transformation above described. The preferred direction of magnetizationof the test piece which had been deformed was found identical to thedirection of the τ_(c) [001] axis, and its magnetic characteristics werefound to be:

    Br = 6,800 G Hc = 1,850 Oe BHmax = 6.9 × 10.sup.6 G.Oe

showing an improved Br, as compared with the magnetic characteristic inthe preferred direction of magnetization observed before thedeformation. Besides, it was determined that it is hard to cause theτ_(c) → ε_(c) ' transformation at a temperature other than 50°C abovethat which causes ε_(c) ' → τ_(c) transformation, and that deformationvelocity of test piece in ε_(c) ' ⃡ τ_(c) transformation increases withtemperature rise up to 750°C.

EXAMPLE 7

From a monocrystal in the ε_(c) phase having a composition of Mn 71.95%,Al 26.95% and C 1.10%, as chemically analyzed, which had beenmanufactured by a method similar to that of Example 1, cubic orrectangular test pieces having varied crystalline surfaces and sides of5 - 12 mm were cut out, and each test piece was put to the similar testsas those of Examples 3 and 4. Then, results showing qualitatively thesimilar tendencies as observed in Examples 3 and 4 in the relationshipbetween the pressuring direction and the degree of deformation, therelationship between the pressuring direction and the degree ofanisotropization, etc., were observed and the existence of the ε_(c) 'phase, was confirmed by way of X-ray diffraction.

The experimental results obtained with a test piece in the ε_(c) phasehaving no lamellar Mn₃ AlC phase, as compared with the test results withthe test pieces of Examples 3 and 4 in which Mn₃ AlC was separated inlamellae, showed that its deformability was low, accordingly that, whilein the cases of Examples 3 and 4, pressure of only 15 - 40 kg/mm² wererequired for making the deformation, in this case, a pressure of 35 - 60kg/mm² being several ten percentages larger than those above mention wasneeded, and that even the anisotropic magnet, because of the loworientation in its τ_(c) phase, was found to be an anisotropic magnetwith inferior magnetic characteristics to those of Examples 3 and 4.

For example, as a monocrystalline ε_(c) test piece consisting of theabove-mentioned composition was pressured in the pressuring direction ofθ₁ = 90°, θ₂ = 0° and under the condition of the pressuring temperaturebeing 560°C and the pressuring force 50 kg/mm², the degree ofdeformation in the pressuring direction was found to be -1.9%, and themeasurements of its magnetic characteristics showed it to be quitenon-magnetic. As the test piece which had been pressured was examined byway of X-ray diffraction in varied directions, only the diffractionpattern from the ε_(c) ' phase was observed, and it was found to haveits ε_(c) ' [001] axis mainly in the pressuring direction, but was notidentified as a monocrystal. Then, as its phase was observed under anoptical microscope, a structure nearly criss-crossing was recognized inthe surface of the test piece, and a crystal in the ε_(c) ' phasediffering in crystalline azimuth was observed. As the test piece whichhad been pressured was subjected to a tempering at 570°C for 4 hours, ananisotropic magnet with its preferred direction of magnetization in thepressuring direction was obtained.

Its magnetic characteristics were found in the pressuring direction tobe:

    Br = 5,450 G .sub.B Hc = 2,200 Oe BHmax = 3.3 × 10.sup.6 G.Oe

In the direction at a right angle to the pressuring direction andcorresponding to the [1120] direction before making the pressuring themagnetic characteristics were:

    Br = 1,000 G .sub.B Hc = 600 Oe BHmax = 0.2 × 10.sup.6 G.Oe

In another direction at a right angle to the pressuring direction themagnetic characteristics were:

    Br = 2,400 G .sub.B Hc = 1,400 Oe (BH)max = 0.9 × 10.sup.6 G.Oe

Comparing these values of magnetic characteristics with those ofmagnetic characteristics obtained in the similar experiment in Example4, Br was found about 20% lower in the preferred direction ofmagnetization, (BH)max about one half, and the degree of angularity ofthe magnetization curve in the second quadrant was lessened, showing alowered degree of anistropizaiton from that of Example 4.

Moreover, even when the above-mentioned conditions of the pressuringtemperature, pressuring force and the degree of deformation, and thetempering condition after making the pressuring were altered, anyfurther improvement in the magnetic characteristics was recognized.

Furthermore, when the pressuring direction was widely varied, every testpiece, as compared with those of Example 4, gave magneticcharacteristics of Br being about 10 - 30% lower and (BH)max about onehalf, showing an essential difference due to the existence of the Mn₃AlC phase from the results of Example 4.

As the causes of the difference in the magnetic characteristics betweenExample 4 and Example 7 were examined by way of optical microscope andX-ray diffraction, it was determined that in the process of warmdeformation of Example 4, the lamellar Mn₃ AlC phase had the effect ofenhancing the orientation of the ε_(c) ' phase by subduing the evolutionof such multi-directional ε_(c) ' phases as the twin of the matrix ε_(c)' phase, and accordingly, the orientation of the matrix τ_(c) phase,after being tempered, as observed in Example 4, was superior to that ofExample 7, showing a remarkable improvement in magnetic characteristicsover the results of Example 7.

As described hereabove, the Mn₃ AlC phase separated out in lamellae bythe M treatment has not only the effect of facilitating the sliding ofthe plane of atoms in the Mn-Al-C alloys, thereby making the warmdeformation with a low pressure feasible, but also the effect ofenhancing the directionalization by controlling the azimuth in theformation of the crystal. Accordingly, it became evident that theexistence of the lamellar Mn₃ AlC phase is very important in theobtention of anisotropic magnets high in the degree of anisotropizationand having quite excellent magnetic characteristics.

EXAMPLE 8

An attempt was made to manufacture the ε monocrystal from an Mn-Al alloyhaving a composition of Mn 71.81%, Al 28.19%, as chemically analyzed, bythe melting and cooling method, as in Example 1. The alloy obtained wasa polycrystal in which the remaining ε phase was very small in amount;the most part consisted of the β-Mn phase and the AlMn(γ) phase, andsome part was recognized to be the τ phase. A nearly similar tendency asabove mentioned was observed when the composition of Mn and Al, meltingconditions and cooling conditions were widely varied, and notable cracksdeveloped when the alloy was quenched into water from such a highertemperature as above 900°C in order to obtain the ε phase. On the otherhand, when a Mn-Al binary alloy of the same composition, as mentionedabove, was heated for one week at a temperature of 1,100° - 1,200°C, toaccelerate its recrystallization as the ε phase, and was then quenchedinto water from this temperature, the test speciment had heave cracks,but the ε phase having particle diameters of about 3 - 5mm could beobtained. From this crystal in the ε phase, cubic test pieces of 3 × 3 ×3 mm having surfaces parallel to (3304), (1120) and (3308) which werechosen from among parts having relatively large crystalline grains werecut out, and were pressured to a degree of deformation of -14.7% under acondition of pressuring with a force of 40 kg/mm², at a temperature of530°C in the direction of θ₁ = 55° and θ₂ = 0°, i.e., in the directionperpendicular to the (3304) plane.

The test piece was found out to be an isotropic magnet; its elongationwas isotropic, and its magnetic characteristics were:

    Br = 1,350 G .sub.B Hc = 650 Oe BHmax = 0.2 × 10.sup.6 G.Oe

As the test speciment after being deformed was examined by way of X-raydiffraction, the existence of the diffracted lines from the τ phase,β-Mn phase and AlMn(γ) phase was evident, but the orientation of the τphase was barely recognizable.

Even when the pressuring temperature, the pressure and the degree ofdeformation were widely varied, the similar tendency as above mentionedprevailed, and test pieces being in the τ phase only could not beobtained, which evidences lack of anisotropization. This result isbelieved to be due to the low stability of the ε phase and the τ phase.Also, it is difficult that in the Mn-Al alloys, unlike the Mn-Al-Calloys, the τ phase exists at above 530°C, and also their decompositionto the AlMn(γ) phase and the β-Mn phase is accelerated by the warmdeformation. Moreover, the directional control effect by the lamellarMn₃ AlC phase above described is absent.

EXAMPLE 9

A monocrystal or a polycrystal within large crystalline grains in the εor ε_(c) (M) phase of Mn-Al-C alloys with its composition of Mn, Al andC varied within the range of Mn 67.0 - 74.0% and C 0.1 - 2.5% wasmanufactured, and from these crystals, monocrystal test pieces in the εor ε_(c) (M) phase were cut out, and were then pressured at 40 kg/mm² ata temperature of 570°C in the direction of θ₁ = 55° and θ₂ = 0° .

In Table 4, the values of compositions obtained by chemical analysis andthe values of magnetic characteristics in the preferred direction ofmagnetization measured after tempering following the pressuring, arerespectively shown.

The test pieces of S₂₃ and S₂₄ containing carbon in amounts fallingshort of its solubility limit (1/10M-6.6)% were barely turnedanisotropic, and with the AlMn(γ) phase and the β-Mn phase separated,their magnetic characteristics were low in isotropy. The test piece ofS₂₅ had a large amount of the β-Mn phase, and that of S₃₀ a plenty ofthe AlMn (γ) phase; both were low in the degree of anisotropization, andgave low magnetic characteristics. All the test specimens of S₃₁, S₃₂,and S₃₃ containing carbon in amounts in excess of (1/3Mn -- 22.2)% hadan Al₄ C₃ phase already before being deformed, were low in the degree ofanisotropization even after being deformed, and gave nearly isotropicmagnetic characteristics. In all these test specimens, S₃₁, S₃₂ and S₃₃,the decaying phenomenon was recognized. In test specimen S₂₉, theAlMn(γ) phase was slightly recognized.

Even when the pressuring condition of direction, temperature and degreeof deformation and the tempering condition were varied in conducting theexperiment with test pieces giving less than BHmax = 2.0 × 10⁶ G.Oe,only such low magnetic characteristics as below BHmax = 2.0 × 10⁶ G.Oewere achieved.

                  Table 4                                                         ______________________________________                                        Mn        Al      C      Br    B.sup.HC                                                                            (BH)max                                  (%)       (%)     (%)    (G)   (Oe)  (× 10.sup.6 G.Oe)                  ______________________________________                                        S.sub.23                                                                            72.02   27.43   0.55 1400   900  0.4                                    S.sub.24                                                                            69.77   30.04   0.19 1100   550  0.2                                    S.sub.25                                                                            73.44   25.53   1.03 2500  1250  0.9                                    S.sub.26                                                                            72.89   25.86   1.25 6450  2350  6.4                                    S.sub.27                                                                            71.58   27.22   1.20 6900  2250  9.0                                    S.sub.28                                                                            70.72   28.29   0.99 6750  2200  8.0                                    S.sub.29                                                                            68.14   31.41   0.45 6550  1900  6.8                                    S.sub.30                                                                            67.63   32.17   0.20 1800   850  0.5                                    S.sub.31                                                                            71.40   26.42   2.18 2500  1400  1.1                                    S.sub.32                                                                            70.78   27.77   1.45 2750  1300  1.1                                    S.sub.33                                                                            69.90   28.77   1.33 2600  1250  1.0                                    ______________________________________                                    

From the experimental results described hereabove, it became evidentthat to attain excellent magnetic characteristics higher than BHmax =6.0 × 10⁶ G.Oe, the composition should be limited to the followingranges:

Mn 68.0 - 73.0%

C (1/10mn - 6.6) - (1/3Mn - 22.2)%

Al remainder

EXAMPLE 10

Mn 72%, Al 27% and C 1% were mixed. The mixture was melted at about1,400°C for 20 minutes, and was then, cast in a chill mold. The castingobtained had Mn 71.83%, Al 27.19% and C 0.98%, as chemically analyzed,and columnar crystals were observed under an optical microscope in theinitially solidified parts. As this casting was subjected to the Mtreatment at 850°C for 20 minutes, and was then, quenched from thistemperature, a separation of lamellar Mn₃ AlC was recognized in thecolumnar crystalline grains the lamellar pattern showing aboundingcrystalline grains which makes about a right angle to the growingdirection of the columnar crystals. As this casting was examined by wayof X-ray diffraction, the diffracted lines from the ε_(c) phase and thelamellar Mn₃ AlC phase were detected.

From this casting, a cubic test piece of 6 × 6 × 6 mm having a surfaceperpendicular to the growing direction of the columnar crystal was cutout, and then was pressured under a temperature of 650°C and pressure of45 kg/mm². The degree of deformation of the test piece in the pressuringdirection was found to be -25.5%. The test piece after being pressuredwas nonmagnetic, but when tempered at 570°C for 4 hours, it turned intoan anisotropic magnet with its preferred direction of magnetization at aright angle to the pressuring direction. Its magnetic characteristics,as measured in the pressuring direction, were found to be:

    Br = 2,800 G .sub.B Hc = 1,500 Oe (BH).sub.max = 1.1 × 10.sup.6 G.Oe

In one direction at a right angle to the pressuring direction andparallel to the growing direction of the columnar crystal before beingpressured the magnetic characteristics were:

    Br = 4,300 G Hc = 2,350 Oe (BH).sub.max = 3.6 × 10.sup.6 G.Oe

In another direction at a right angle to the pressuring direction:

    Br = 4,750 G Hc = 2,400 Oe (BH).sub.max = 4.9 × 10.sup.6 G.Oe

EXAMPLE 11

Rod shape castings of 9 kinds of Mn-Al-C alloys, P₁ - P₉, having thecomposition ratios listed in Table 5, were manufactured by melting andcasting. Melting was performed by holding at temperature of 1,430°C for30 minutes to melt carbon well into its solid solution. Cylindrical testpieces of 20mmφ × 25mm were respectively cut out from them. Then, aftersubjecting each test piece cut out to the heat treatment in which afterheating it at a temperature of 1,150°C for 2 hours, it was graduallycooled from this temperature to 830°C at a cooling rate of 10° -15°C/min, and was then held at 830°C for 20 minutes, it was quenchedfrom 830°C at a cooling rate of 300° - 3,000°C/min. and was furthersubjected to a heat treatment of tempering at 600°C for 1 hour. As eachtest specimen which had been subjected to the heat treatment wasexamined as to its phase structure by way of X-ray diffraction, opticalmicroscopy and electron microscopy, in the test pieces of thecompositions of P₃ - P₉ containing carbon in excess of its solubilitylimit (1/10 Mn -- 6.6)%, the lamellar Mn₃ AlC phase and/or face centeredcubic phase being similar thereto and more especially, in test pieces ofthe composition of P₃, P₄ , P₅, P₈, was recognized clearly. But in thetest pieces of the compositions of P₁ - P₂ with the amount of carbonfalling short of the solubility limit, the lamellar Mn₃ AlC phase and/orface centered cubic phase being similar thereto was not seen at all. Inthe test pieces of the compositions of P₈ P₉ with the amount of carbonrunning in excess of (1/3 Mn - 22.2)%, a separation of Al₄ C₃, inaddition to the τ_(c) phase and lamellar Mn₃ AlC, and/or face centeredcubic phase being similar thereto, was observed, and in the test pieceof the composition of P₃, the β-Mn phase, and in the test piece of thecomposition of P₇, the AlMn(γ) phase, were respectively found existingin a large amount. In test piece of composition of P₆, and AlMn(γ) phasewas recognized slightly.

These test specimens were respectively subjected to the following warmdeformation.

A test piece having the composition of P₁ is compressed by pressuring itat a temperature of 680°C, a pressure of 50 kg/mm² and in the axialdirection of the cylinder to a degree of deformation of -25% in thepressuring direction. In the test piece which had been subjected to thedeformation, numerous cracks were found developing. Its magnetic

                  Table 5                                                         ______________________________________                                                Mn        Al          C                                               ______________________________________                                        P.sub.1   72.08       27.45       0.47                                        P.sub.2   70.21       29.55       0.24                                        P.sub.3   73.44       25.51       1.05                                        P.sub.4   72.36       26.40       1.24                                        P.sub.5   71.63       27.23       1.14                                        P.sub.6   68.86       30.78       0.40                                        P.sub.7   67.86       31.81       0.33                                        P.sub.8   71.66       26.35       1.99                                        P.sub.9   69.90       28.67       1.43                                        ______________________________________                                         characteristics greatly declined from the characteristic of (BH).sub.max =     0.6 × 10.sup.6 G.Oe, as measured before making the pressuring, to:

    Br = 1,700 G .sub.B Hc = 700 Oe (BH).sub.max = 0.3 × 10.sup.6 G.Oe

showing it to be isotropic. As this test piece was examined by way ofX-ray diffraction, large amount of the β-Mn phase and AlMn(γ) phase wererecognized, other than a small amount of remaining τ phase, and theadditional heat treatment of tempering merely caused a further declinein its magnetic characteristics.

A test piece having the composition of P₂ was subjected to a deformationto the degree of deformation of -50% by pressuring it at a temperatureof 710°C, a pressure of 55 kg/mm² and in the axial direction of thecylinder. The test piece which had been subjected to this deformationwas found to be pulverized, and its lumpy grains showed barely anymagnetism, as a magnet approached it. As this test piece which had beensubjected to this deformation was examined by way of X-ray diffraction,the existence of the τ phase was not recognized at all; only the AlMn(γ)phase and the β-Mn phase were detected. This is believed to be due tothe fact that its decomposition from the τ phase to the AlMn(γ) phaseand β-Mn phase was accelerated by this warm deformation just as in thecase of P₁ above described.

A test piece having the composition of P₃ was subjected to a compressiondeformation to a degree of deformation of -40% by pressuring it at apressure of 50 kg/mm², at a temperature of 630°C and in the axialdirection of the cylinder. The test piece which had been subjected tothis deforming showed its preferred direction of magnetization in thedirection of its diameter but the magnetic characteristics found in thisdirection were only;

    Br = 2,600 G .sub.B Hc = 1,500 Oe (BH).sub.max = 1.0 × 10.sup.6 G.Oe

Thus, its magnetic characteristics were not improved even by anadditional tempering treatment. As the test piece which had beensubjected to this deforming was examined by way of X-ray diffraction,the β-Mn phase was noted in a large amount, which was believed to haveworked against the upgrading of its magnetic characteristics.

A test piece having the composition of P₄ was extruded to a degree of65%, at a pressure of 40 kg/mm² and a temperature of 720°C, and in theaxial direction of the cylinder. The degree of extrusion is expressed bythe percentage of the decrease in the sectional area of the test piece,as measured before and after being extruded. The test piece which hadbeen subjected to the extrusion was found to be an excellent anisotropicmagnet with its preferred direction of magnetization in the axialdirection of the extruding direction, namely, the axial direction of thecylindrical test piece, and its magnetic characteristics in thepreferred direction of magnetization were:

    Br = 6,100 G .sub.B Hc = 2,200 Oe (BH).sub.max = 5.5 × 10.sup.6 G.Oe

As the test piece which had been subjected to the extrusion was examinedas to its phase structure by way of X-ray diffraction and opticalmicroscopic observation, it was found to be in the τ_(c) phase and thelamellar Mn₃ AlC phase, and a streak pattern of the lamellar Mn₃ AlCphase nearly parallel to the extruding direction was noticed. A testpiece having the composition of P₄ was subjected to a compression to adegree of deformation of -53% by applying a pressuring force of 45kg/mm² in the axial direction of its cylinder at 650°C. The preferreddirection of magnetization of the deformed specimen was found in thediameter direction of it, with its magnetic characteristics being:

    Br = 4,900 G .sub.B Hc = 2,600 Oe (BH).sub.max = 4.3 × 10.sup.6 G.Oe

A test piece having the composition of P₅ was subjected to a compressionto a degree of deformation of -65%, by applying a pressuring force of 45kg/mm² in the axial direction of its cylinder at 680°C. The preferreddirection of magnetization of the deformed specimen was found in thediameter direction of it, with its magnetic characteristics being:

    Br = 5,050 G .sub.B Hc = 2,600 Oe (BH).sub.max =  4.6 × 10.sup.6 G.Oe

A test piece having the composition of P₅ was subjected to an extrusionto a degree of extrusion of 65% by applying a pressuring force of 40kg/mm² in the axial direction of its cylinder at 630°C. The preferreddirection of magnetization of the extruded specimen was found in theextruding direction with its magnetic characteristics being:

    Br = 5,850 G .sub.B Hc = 2,250Oe (BH).sub.max =  5.7 × 10.sup.6 G.Oe

The test pieces having the composition of P₅ were subjected to anextrusion to a degree of extrusion of 50% in the axial direction of itscylinder, with the extruding temperature varied in the range of 500°C to850°C. Table 6 shows the relation between the extruding temperature andthe magnetic properties in the preferred direction of magnetization.Below the extruding temperature of 500°C, just as in the case ofExamples 4, the test piece had little plasticity; its extrusion wasdifficult; the development of cracks was notable, and it failed tobecome anisotropic. At a temperature above 830°C also, it showeddecreasing plasticity, with accompanying cracks, and failed to becomeanisotropic. Then in the range of extruding temperature of 580° - 830°C,excellent anisotropic magnets giving (BH)_(max) higher than 4.8 × 10⁶G.Oe were obtained.

                  Table 6                                                         ______________________________________                                        Temperature Br       B.sup.Hc (BH)max                                         (°C) (G)      (Oe)     (× 10.sup.6 G.Oe)                         ______________________________________                                        500         2,700    1,400    1.1                                             580         5,650    2,050    5.0                                             630         6,050    2,150    5.6                                             730         6,000    2,100    5.5                                             830         5,500    2,000    4.8                                             850         2,550    950      0.7                                             ______________________________________                                    

A test piece having the composition of P₆ was subjected to an extrusionby to the degree of extrusion of 31% pressuring with a force of 40kg/mm² at a temperature of 700°C and the axial direction of itscylinder. The test piece which had been subjected to this working showedthe following magnetic characteristics in the extruding direction.

    Br = 4,350 G .sub.B Hc = 1,600 Oe (BH).sub.max = 2.4 × 10.sup.6 G.Oe

As this test piece which had been subjected to extrusion was furtherextruded to a degree of extrusion of 25% by applying a pressuring forceof 25 kg/mm² in the same direction at a temperature of 700°C, itsmagnetic characteristics in the extruding direction were found to be:

    Br = 5,700 G .sub.B Hc = 1,950 Oe BH.sub.max =  5.0 × 10.sup.6 G.Oe

A test piece having the composition of P₇ was extruded to a degree ofextrusion of 50% by applying a pressuring force of 45 kg/mm² in theaxial direction of its cylinder at a temperature of 780°C. On the testpiece which was subjected to this extrusion, cracks developed nearlyperpendicular to the extruding direction. Its magnetic characteristicsin the extruding direction, thus its preferred direction ofmagnetization, were found to be:

    Br = 2,750 G .sub.B Hc = 1,700 Oe (BH).sub.max =  1.8 × 10.sup.6 G.Oe

A test piece having the composition of P₈ was subjected to a compressionto a degree of deformation of -76% by applying a pressuring force of 50kg/mm² in the axial direction of its cylinder at a temperature of 750°C.On the test piece which was subjected to this compression, cracksdeveloped in the diameter direction around its perimeter. Its preferreddirection was found in the diameter direction of the test piece, withits magnetic characteristics being:

    Br = 3,800 G .sub.B Hc = 1,800 Oe (BH).sub.max =  2.1 × 10.sup.6 G.Oe

This test piece had Al₄ C₃ separated in it, and began disintegratingseveral days thence. A test piece having the composition of P₉ wassubjected to a compression to a degree of deformation of -35% byapplying a pressuring force of 55 kg/mm² in the axial direction of itscylinder at 700°C. Its preferred direction of magnetization of thedeformed specimen was found in the diameter direction of it, with itsmagnetic characteristics being:

    Br =  3,400 G .sub.B Hc = 1,700 Oe (BH).sub.max =  1.9 × 10.sup.6 G.Oe

This specimen had Al₄ C₃ separated in it, and began disintegratingseveral days thence.

As demonstrated by the examples above described, the test pieces beingin the phase of τ_(C) (M) showed excellent plasticity in the temperaturerange of 530° - 830°C, and become highly anisotropic by the warmdeformation and thus, these test pieces were identified as anisotropicmagnets having very excellent magnetic characteristics. On the otherhand, when the lamellar Mn₃ AlC phase was absent in the test pieces orwhen phases other than the τ _(c) phase, for example, the phases of Al₄C₃, β-Mn or AlMn(γ(γ) existed, their plasticity was found improper; thedegree of their anisotropization was also slight, and their magneticcharacteristics were low.

Accordingly, as the condition for obtaining excellent anisotropicmagnets, it is necessary to have their compositions falling within theranges of Mn 68.0 - 73.0%, C (1/10Mn -- 6.6)% - (1/3 Mn -- 22.2)% andremainder Al, preferably within the ranges of Mn 70.5 - 72.5%, C(1/10 Mn-- 6.6) - (1/3 Mn - 22.2)% and the remainder Al. Also, it is necessaryto subject the τ_(c) (M) phase with such composition ranges to a warmplastic deformation in the temperature range of 530°-830°C, especiallyby an extrusion to a degree of 40 - 65%. The resultant anisotropicmagnets have excellent magnetic characteristics, i.e. (BH)_(max) higherthan 4.8 × 10⁶ G.Oe. Furthermore, the mechanical strength measured afterthe warm deformation showed a marked improvement, and also themachinability was excellent.

EXAMPLE 12

From a casting similar to that of Example 11 having a composition of P₅,a cylindrical test piece of 20 mmφ × 35 mm was cut out. After holding itat a temperature of 1,000°C for 5 hours, it was cooled to 835°C at acooling rate of 10°C/min., and then further quenched from thistemperature at a cooling rate of 300°- 3,000°C/min. Then, as this testpiece was held at 500°C for 10 minutes, it was confirmed by way of X-raydiffraction and optical microscopic observation of its phase structurethat about 70% was the ε_(c) (M) phase, and the remaining about 30%, theτ_(c) (M) phase.

This test piece was extruded to a degree of extrusion of 40% by applyinga force of 40 kg/mm² at a temperature of 730°C in the axial direction ofits cylinder. As the magnetic characteristics in the extruding directionof the test piece after being extruded were found low, and the existenceof the ε_(c) ' phase was recognized by the X-ray diffraction, then itwas further tempered at 600°C for 2 hours. In this way, an anisotropicmagnet having very excellent magnetic characteristics with its preferreddirection of magnetization in its axial direction was obtained. Itsmagnetic characteristics in the preferred direction of magnetizationwere found to be:

    Br = 6,200 G .sub.B Hc = 2,300 Oe (BH).sub.max =  6.0 × 10.sup.6 G.Oe

The test piece had a very high mechanical strength and machinabilityafter extrusion, giving values equal or higher than those obtained inExamples 11.

EXAMPLE 13

From the same casting of Example 11 having the composition of P₅, acylindrical test piece of 20φ × 35 mm was cut out, cooled down to1,000°C after holding it at a temperature of 1,150°C for 2 hours, andthen quenched from this temperature at a cooling rate within the range300° - 3,000°C./min.

This test piece in the ε_(c) phase after being quenched was extruded toa degree of extrusion of 40% by applying a pressuring force of 60 kg/mm²at a temperature of 730°C in the axial direction of its cylinder. Itsdeformation velocity was lower than that in the extrusion of the τ_(c)(M) phase test piece of the same composition of Example 11, showing lowdeformability. The test piece, after being extruded, was found to be inthe ε_(c) phase and ε_(c) ' phase, as examined by way of X-raydiffraction.

The magnetic characteristics of the test piece after being extruded, asmeasured after tempering it at 600°C for 2 hours, were found, in theextruding direction, to be:

    Br = 5,200 G .sub.B Hc = 1,950 Oe (BH).sub.max = 4.8 × 10.sup.6 G.Oe

It was identified as an anisotropic magnet with its preferred directionof magnetization in the extrusion direction. This test piece had a veryhigh mechanical strength and machinability, giving values equal orhigher than those obtained in Examples 11 and 12.

EXAMPLE 14

From the same castings of Example 11 having the compositions of P₁ -P₉listed on Table 5, cylindrical test pieces of 20mmφ × 35 mm wererespectively cut out. These test pieces were gradually cooled down to830°C at a cooling rate of 10°C/min. after holding them at 1,150°C for 2hours, and then they were subjected to the M treatment in which theywere held at a temperature of 830°C for 20 minutes, subsequently theywere quenched at a cooling rate of 1,000°C./min from this temperature.

As the phase structure of these test pieces after being quenched wereexamined by way of X-ray diffraction, optical microscopy and electronmicroscopy, in the test pieces of the compositions of P₃ - P₉ containingcarbon in excess of its solubility limit of (1/10 Mn -- 6.6) %, thelamellar Mn₃ AlC phase and/or face centered cubic phase being similarthereto was recognized, but in the test pieces of the compositions of P₁and P₂ containing carbon falling short of its solubility limit, thelamellar Mn₃ AlC phase and/or face centered cubic phase being similarthereto was not seen at all. In the test pieces of the compositions ofP₈ and P₉ containing carbon in excess of (1/3 Mn -- 22.2) %, theexistence of Al₄ C₃, besides the ε_(c) phase and the lamellar Mn₃ AlCphase and/or face centered cubic phase being similar thereto wasnoticed. Then, in the test piece of the composition of P₃, the β-Mnphase, and in the test piece having the composition of P₇, the AlMn (γ)phase, were respectively much observed. The test piece having thecomposition of P₁ was found to have a small amount of the ε phase andlarge amounts of the AlMn (γ) phase and the β-Mn phase, while in thetest piece of the composition of P₂, nearly equal amounts respectivelyof the τ phase, β-Mn phase and AlMn (γ) phase existed in admixture, butthe ε phase was not detected at all.

These test pieces after being heat treated were respectively subjectedto the warm deformation described hereinafter, and then furthersubjected to tempering suitable for respective test pieces.

A test piece having the composition of P₁ was extruded to a degree ofextrusion of 40% by applying a pressure of 50 kg/mm² at a temperature of630°C in the axial direction of its cylinder. The test piece after beingextruded was in the state of being pulverized into lumpy grains of o.5 -2 mm, not retaining its original configuration. From large grains ofthem, a piece the size of 1 mm cubic was cut out, to be further temperedat 500°C for 30 minutes. Measurements of its magnetic characteristicsshowed it to be isotropic, giving the following values:

    Br = 1,200 G .sub.B Hc = 400 Oe (BH)max = 0.1 × 10.sup.6 G.Oe

The results of examination of this test piece by way of X-raydiffraction showed that it was mostly in the β-Mn phase and the AlMn (γ)phase, with the remnant of the τ phase being small. This is believed tobe because the decomposition from the ε phase and the τ phase to theAlMn (γ) phase and the β-Mn phase was accelerated by the warmdeformation.

A test piece having the composition of P₂ was compressed to a degree ofdeformation of -20% by applying a pressuring force of 45 kg/mm² at atemperature of 780°C in the axial direction of its cylinder. The testpiece, after being compressed was found to be pulverized, not retainingits original shape. The results of examination of this test piece afterbeing compressed showed no existence of the τ phase, but only the AlMn(γ) phase and the β-Mn phase were recognized. This is believed to bebecause the decomposition from the τ phase to the AlMn (γ) phase and theβ-Mn phase was accelerated by the warm deformation.

A test piece having the composition of P₃ was compressed to a degree ofdeformation of -50% by applying a pressuring force of 40 kg/mm² at atemperature of 580°C in the axial direction of its cylinder. On the testpiece after being compressed, a small number of cracks were detected inits diameter direction around its perimeter, its magnetism being slight.The magnetic characteristics of this test piece, as measured aftertempering it at 570°C for 3 hours, showed its preferred direction ofmagnetization in its diameter direction, but were such low values as:

    Br = 2,580 G Hc = 1,400 Oe BHmax = 1.3 × 10.sup.6 G.Oe

The results of examination of the test pieces after being compressed andafter being tempered showed it to have a large amount of the β-Mn phase,and this seems to account for the failure to achieve an improvement inits magnetic characteristics.

A test piece having the composition of P₄ was extruded to a degree ofextrusion of 50% by applying a pressure of 40 kg/mm² at a temperature of720°C in the axial direction of its cylinder. The test piece, afterbeing extruded, by way of X-ray diffraction showed the existence of theε_(c) ' phase, besides the Mn₃ AlC phase. The magnetic characteristicsof this test piece, as measured after tempering it at 550°C for 10hours, were found in the extruding direction to be:

    Br = 6,400 G .sub.B Hc = 2,550 Oe (BH)max = 6.2 × 10.sup.6 G.Oe

It was identified as a very excellent anisotropic magnet with itspreferred direction of magnetization in the extrusion direction. As thephase structure of this test piece was examined by way of X-raydiffraction and optical microscopic observation, it was found to be inthe τ_(c) phase and the Mn₃ AlC phase, and the streak pattern of thelamellar Mn₃ AlC phase running nearly parallel to the extrudingdirection was observed.

A test piece having the composition of P₄ was compressed to a degree ofdeformation of -45% by applying a pressuring force of 45 kg/mm² at atemperature of 650°C in the axial direction of its cylinder. The testpiece after being compressed was tempered at 600°C for 3 hours, and thenas the result of the measurement of its magnetic characteristics, it wasidentified as an anisotropic magnet with its preferred directionmagnetization in its diameter direction. Its magnetic characteristics inthe preferred direction of magnetization were found to be: pressuring

    Br = 5,300 G .sub.B Hc = 2,600 Oe (BH)max = 4.7 × 10.sup.6 G.Oe

A test piece having the composition of P₅ was extruded to degree ofextrusion of 50% by applying a pressure of 45 kg/mm² at a temperature of630°C in the axial direction of its cylinder. As examined aftertempering it at 550°C for 20 hours, it was identified to be ananisotropic magnet with its preferred direction of magnetization in theextruding direction, its characteristics were:

    Br = 6,250 G .sub.B Hc = 2,500 Oe (BH)max = 6.3 × 10.sup.6 G.Oe

    4πI.sub.10000 =  6,800 G .sub.I Hc = 2,800 Oe Br/4πI.sub.10,000 = 0.92

a test piece having the composition of P₅ was extruded to a degree ofextrusion of 40% in the axial direction of its cylinder, with thetemperature varied in the range of 500°C to 850°C. In Table 7, itsmagnetic characteristics in the extruding direction as measured upontempering it after the extruding, related to the working temperature,were shown. When the deforming temperature was below 500°C, it hadlittle plasticity, just as in the cases of Examples 4 and 11, thusposing difficulty in its extrusion, showed notable development ofcracks, and was not turned anisotropic by the tempering. Even attemperatures above 830°C, it showed a diminishing plasticity, withaccompanying development of cracks, and failed to become anisotropic. Inthe temperature ranges of 530°- 830°C, an excellent anisotropic magnetwith (BH)max higher than 5.2 × 10⁶ G.Oe was obtained at a lower degreeof extrusion than in the case of Example 11.

                  Table 7                                                         ______________________________________                                        deforming temperature                                                                       Br      B.sup.Hc                                                                              (BH)max                                         (°C)   (G)     (Oe)    (× 10.sup.6 G.Oe)                         ______________________________________                                        500           2700    1200    1.0                                             530           6000    1950    5.5                                             630           6300    2450    6.3                                             730           6150    2200    6.1                                             830           5700    2000    5.1                                             850           2800    1350    1.2                                             ______________________________________                                    

A test piece having the composition of P₆ was extruded to a degree ofextrusion of 31% by applying a pressure of 40 kg/mm² at 650°C in theaxial direction of its cylinder. After being extruded, it was temperedat 620°C for 2 hours, then was identified as an anisotropic magnet withits preferred direction of magnetization in the extrusion direction. Itsmagnetic characteristics in that direction were found to be:

    Br = 6,300 G .sub.B Hc = 2,150 Oe (BH).sub.max = 5.3 × 10.sup.6 G.Oe

A test piece having the composition of P₇ was compressed to a degree ofdeformation of -35% by applying a pressuring force of 45 kg/mm² at atemperature of 800°C in the axial direction of its cylinder. The testpiece after being compressed was tempered at 550°C for 12 hours, and itwas identified as an anisotropic magnet with its preferred direction ofmagnetization in the diameter direction. Its magnetic characteristics,however, were found to give such low values as:

    Br = 1,950 G .sub.B Hc = 1,050 Oe (BH).sub.max =  0.7 × 10.sup.6 G.Oe

A test piece having the composition of P₈ was compressed to a degree ofdeformation of -18% by applying a pressuring force of 50 kg/mm² at atemperature of 730°C in the axial direction of its cylinder. The testpiece after being compressed was tempered at 570°C for 6 hours, and itwas identified as an anisotropic magnet with its preferred direction ofmagnetization in the diameter direction. Its magnetic characteristics,however, were found to give such low values as:

    Br = 3,350 G .sub.B Hc = 1,900 Oe (BH).sub.max = 1.7 × 10.sup.6 G.Oe

This test piece began disintegrating several days thence.

A test piece having the composition of P₉ was extruded to a degree ofextrusion of 31% by applying a pressure of 55 kg/mm² at 780°C in theaxial direction of its cylinder. The test piece after being extruded hadlamellar cracks perpendicular to the extrusion direction. Aftertempering this alloy at 600°C for 4 hours, it was identified as ananisotropic magnet with its preferred direction of magnetization in theextrusion direction, but its magnetic characteristics were found to besuch low values as:

    Br = 3,700 G Hc = 2,200 Oe (BH).sub.max = 2.1 × 10.sup.6 G.Oe

This test piece, too, began disintegrating several days thence.

Furthermore, as disc test pieces with their preferred direction ofmagnetization in the direction parallel to the disc surface were cut outfrom the respective test pieces having the above mentioned magneticcharacteristics, and their magnetic torques were measured. Every testpiece gave a unidirectional magnetic torque curve. The magnetic torquesof these test pieces were found falling within the range of 0.63 - 0.86× 10⁷ dyne-cm/cm³. Then, if the degree of anisotropization is expressedby its ratio to the magnetic torque of 1.07 × 10⁷ dyne-cm/cm² of theτ_(c) monocrystal of Example 3, all of these test pieces gave such highdegrees of anisotropization as above about 0.6. Especially the testpiece with (BH)_(max) = 6.3 × 10⁶ G.Oe obtained by extruding an alloy ofthe composition of P₅ was found to have the high magnetic torque of 0.86× 10⁷ dyne-cm/cm³, and be excellent in orientation, and was thusidentified as an anisotropic magnet having a very high degree ofanisotropization.

As shown by the above described examples, the MnAl-C alloys having theε_(c) (M) phase excelled in plasticity in the temperature range of530° - 830°C, and from these alloys, anisotropic magnets having veryexcellent magnetic characteristics were obtained by way of a warmplastic deformation and tempering after this deformation. In theseinstances, at a degree of deformation 20 - 30% lower than in the case ofExample 11, anisotropic magnets having magnetic characteristics equal or10 - 20% superior to those of Example 11, in comparison with themagnetic characteristics of the test piece in the τ_(c) (M) phase ofExample 11 were obtained.

Accordingly, as the condition for obtaining adequate anisotropic magnetshaving a composition falling within the range of Mn 68.0 - 73.0%, C(1/10Mn -- 6.6)%-(1/3 Mn -- 22.2)% and the remainder Al, preferably, withinthe range of Mn 70.5 - 72.5%, C(1/10 Mn -- 6.6)-(1/3 Mn -- 22.2)% andthe remainder Al, it is an indispensable matter in this instance also,and anisotropic magnets having such very excellent magneticcharacteristics as (BH)_(max) higher than 5.2 × 10⁶ G.Oe were obtainedespecially by way of extrusion performed at a degree of extrusion of30 - 50%. Their mechanical strength and machinability, as measured afterthe warm deformation and additional tempering, showed a notableimprovement, reaching results equal or superior to those in the cases ofExamples 11, 12 and 13.

When the magnetic torques of the test pieces having magneticcharacteristics of (BH)_(max) higher than 4.8 × 10⁶ G.Oe obtained in theabove mentioned Examples 11, 12, 13, 14 were measured, they all gavevalues higher than 0.43 × 10⁷ dyne-cm/cm³. These test pieces thus allshowed such high degree of anisotropization as above about 0.4, as thedegree of anisotropization was expressed in terms of the ratio of thesevalues to the constant of magnetic anisotropization of 1.07 × 10⁷dyne-cm/cm³ of the τ_(c) monocrystal of Example 3. Example 15:

The raw materials of Mn, Al and C were properly mixed, were melted atabout 1,450°C in 30 minutes, thereby melting carbon fully into its solidsolution, and were then, cast to form a rod shape casting of a Mn-Al-Calloy. The composition of the casting thus obtained was as shown inTable 8 in terms of the value of its chemical analysis.

                  Table 8                                                         ______________________________________                                        Sample No.   Mn %       Al %       C %                                        ______________________________________                                        1            67.51      32.27      0.22                                       2            67.55      31.95      0.50                                       3            68.03      31.88      0.09                                       4            68.04      31.66      0.30                                       5            67.91      31.66      0.43                                       6            68.04      31.41      0.55                                       7            68.48      31.40      0.12                                       8            68.53      31.27      0.20                                       9            68.49      31.22      0.29                                       10           68.53      30.95      0.52                                       11           68.55      30.80      0.65                                       12           68.45      30.80      0.75                                       13           68.50      30.59      0.91                                       14           69.02      30.85      0.13                                       15           69.00      30.76      0.24                                       16           69.04      30.64      0.32                                       17           68.99      30.49      0.52                                       18           68.97      30.28      0.75                                       19           68.98      30.14      0.88                                       20           69.55      30.35      0.10                                       21           69.50      30.30      0.20                                       22           69.48      30.23      0.29                                       23           69.50      29.95      0.55                                       24           69.53      29.79      0.68                                       25           69.49      29.60      0.91                                       26           69.51      29.40      1.09                                       27           69.97      29.91      0.12                                       28           69.96      29.82      0.22                                       29           69.95      29.72      0.33                                       30           70.04      29.41      0.55                                       31           69.98      29.30      0.72                                       32           69.95      29.12      0.93                                       33           70.06      28.84      1.10                                       34           70.52      29.39      0.09                                       35           70.56      29.26      0.18                                       36           70.47      28.98      0.55                                       37           70.45      28.66      0.89                                       38           71.02      28.07      0.91                                       39           72.05      26.90      1.05                                       ______________________________________                                    

From each of these castings, a test specimen cubic in shape of 10 × 10 ×10 mm was cut off, was turned into the uniform ε phase or ε_(c) phase byway homogenization by heating at 1,150°C for 2 hours and then quenchingfrom 900°C or more at a cooling rate higher than 10°C/min. in thetemperature range of 830°-900°C. After this heat treatment was carriedout, each test specimen was examined by X-ray diffraction, opticalmicroscopy and electron microscopy to determine its phase structure. Theresults were as follows:

1. Test specimens in which the existence of Al₄ C₃ was recognizedincluded those of Nos. 2, 6, 12, 13, 19 and 26.

2. Test specimens of those mentioned in (1) which had a matrix of ε_(c)single phase included those of Nos. 6, 12, 13, 19 and 26.

3. Test specimens in which deposition of AlMn(γ) phase was recognizedincluded those of Nos. 1, 2, 3 and 5.

4. Test specimens other than those mentioned in (1), (2) and (3) wereall found to be ε or ε_(c) single phase.

These test specimens were tempered in the temperature range of 480° -830°C. When the length of tempering time was 30 minutes, the magneticproperties appreciably decreased above 780°C in all test specimens ofNos. 1 - 39. The temperature range where the τ or τ_(c) phase stablyexisted greatly varied depending on the composition; when the temperingtime length was 30 minutes, it was below 750°C.

The magnetic characteristics of each test specimen obtained whentempered at 700°C for 30 minutes were found to be as shown in Table 9.

                  Table 9                                                         ______________________________________                                        Sample No.                                                                             Br (G)   B.sup.HC (Oe)                                                                            (BH)max (× 10.sup.6 G.Oe)                  ______________________________________                                        1         100      50       0.0                                               2         500     150       0.0                                               3        1300     200       0.1                                               4        2600     550       0.5                                               5        1950     500       0.3                                               6        2500     550       0.4                                               7        1450     250       0.1                                               8        2200     450       0.3                                               9        3200     550       0.6                                               10       3200     600       0.7                                               11       3150     600       0.7                                               12       2950     550       0.6                                               13       2750     550       0.5                                               14       1500     250       0.1                                               15       2400     500       0.4                                               16       3250     500       0.6                                               17       3200     650       0.8                                               18       3150     600       0.7                                               19       2900     600       0.6                                               20       1300     200       0.1                                               21       2350     400       0.3                                               22       2450     450       0.4                                               23       3200     600       0.7                                               24       3200     650       0.8                                               25       3000     650       0.7                                               26       2800     600       0.6                                               27       1250     250       0.1                                               28       2300     450       0.3                                               29       2600     450       0.4                                               30       3050     700       0.7                                               31       3100     850       0.9                                               32       2950     900       0.8                                               33       2800     1200      1.0                                               34       1000     200       0.1                                               35       1550     450       0.2                                               36       2700     1150      0.9                                               37       2600     1300      1.0                                               38       3200     1300      1.2                                               39       3150     1400      1.3                                               ______________________________________                                    

As a result of examination of the phase structure of each test specimenof Table 9 after being tempered, it was found out that in each testspecimen of Nos. 1, 2, 3, 5, 7, 14, 20, 27, 34 and 35, i.e., testspecimens of Mn less than 68.0% or C less than 0.2%, the AlMn (γ) phaseor the β-Mn phase, or both, were observed, and the Br of these testspecimens was found to be less than merely 2000 G. On the other hand, intest specimens other than those mentioned above, i.e., test specimens ofMn more than 68.0% and C more than 0.2%, the stability of τ or τ_(c)phase was satisfactory, and Br runs to 2,000 G or more, up to 750°C,when the tempering time was 30 minutes, but as 750°C was exceeded, thetransformation to the AlMn(γ) phase and β-Mn phase began, as confirmedby the X-ray diffraction, optical microscopy and electron microscopy.

For the test specimen of No. 17, the magnetic characteristics andprincipal phase were observed after it was tempered for 30 minutes inthe temperature range of 480° - 830°C. These results are shown in Table10.

                                      Table 10                                    __________________________________________________________________________       Tempering                                                                  Code                                                                             temperature                                                                          Br  B.sup.HC                                                                          (BH)max Phase                                                  (°C)                                                                          (G) (Oe)                                                                              (× 10.sup.6 G.Oe)                                                               structure                                           __________________________________________________________________________    a  480    2600                                                                              400 0.4     τ.sub.c                                         b  500    2800                                                                              450 0.5     τ.sub.c                                         c  550    3000                                                                              560 0.6     τ.sub.c                                         d  600    3200                                                                              650 0.8     τ.sub.c                                         e  650    3200                                                                              650 0.8     τ.sub.c                                         i  700    3200                                                                              650 0.8     τ.sub.c                                         g  750    3150                                                                              600 0.7     τ.sub.c                                         h  780    1800                                                                              500 0.3     τ.sub.c +AlMn(γ)+β-Mn                i  800    1000                                                                              250 0.1     τ.sub.c +AlMn(γ)+β-Mn                j  830     100                                                                               50 0.0     AlMn(γ)+β-Mn+ε.sub.c             __________________________________________________________________________

EXAMPLE 16

From each of castings of Nos. 1 - 39 of Example 15, a cylindrical testspecimen of 20mmφ × 35 mm was cut out. It was subjected to thehomogenization and quenching similarly as in Example 15, and was then,tempered at 600°C for 30 minutes; thereafter, it was extruded by anoil-hydraulic press at an extruding pressure of 12.6 tons, using a diewith a surface reduction percentage of 75% in the temperature range of500° - 800°C.

At an extruding temperature below 530°C, all test specimens werepulverized, so that no test pieces for the measurement of magneticcharacteristics could be taken. At temperatures above 530°C but below600°C, the test pieces either cracked or did not. Even when no crackingoccurred, the deformability was low, and the degree of anisotropization,e.g., the ratio of (BH)_(max) between the extrusion direction and thedirection at a right angle thereto, was small.

In the temperature range exceeding 780°C, in all test specimens, exceptfor No. 38, 39 the transformations to the AlMn(γ) phase and β-Mn phasetook place; the magnetic property rapidly decreased, and the degree ofanisotropization also diminished.

On the other hand, as for the relationship between the composition andthe magnetic characteristics, when C is 0.2 - (1/3 Mn -- 22.2)%, thedegree of anisotropization was high; in the range of 68.0 - 70.5% Mn,and an anisotropic magnet with preferred direction of magnetization inthe extrusion direction was obtained.

With the amount of Mn more than 70.5% but less than 73.0%, only a smalldegree of anisotropization took place or anisotropization did not occur.

The test specimen of No. 17 of Example 15 was subjected tohomogenization and quenching treatment similarly as in Example 15 and toa tempering at 600°C for 30 minutes after a quenching, and in the sameway as in the preceding example, was extruded by an extruding pressureof 12.6 tons at a surface reduction percentage of 75%. The magneticcharacteristics in the extrusion direction obtained after thesetreatments were carried out were as shown in Table 11.

                  Table 11                                                        ______________________________________                                             Processing                                                               Code temperature                                                                              Br (G)   B.sup.HC (Oe)                                                                         (BH)max                                           (°C)                 (× 10.sup.6 G.Oe)                      ______________________________________                                        a    500        --       --      --                                           b    530        3150     1350    1.5                                          c    580        3200     1500    1.8                                          d    590        5050     1650    3.3                                          e    600        6200     1960    5.5                                          f    650        6450     2500    6.7                                          g    700        6450     2550    6.8                                          h    750        6350     2400    6.5                                          i    780        6350     2300    6.3                                          j    790        4950     1900    3.7                                          k    800        2300     1300    0.8                                          ______________________________________                                    

The test specimen of code a was pulverized, so that its magneticcharacteristics could not have been measured. The test specimens ofCodes b, c and k were almost isotropic, and the test specimens of d andj were lower in the degree of anisotropization than those of e - j.

That is to say, only by the warm deformation at 600° - 780°C, preferably650° - 780°C, anisotropic magnets showing a high degree of anisotropywere obtained.

All of the test specimens of Nos. 1 - 39 of Example 15 were tempered at600°C for 30 minutes after subjecting them to the homogenization andquenching similarly as in Example 15, and were then, extruded at 700°Cby a pressure of 12.5 tons with a surface reduction percentage of 75%.The magnetic characteristics in the extrusion direction of the testspecimen treated in this way were as shown in Table 12.

                  Table 12                                                        ______________________________________                                        Sample No.                                                                             Br (G)   B.sup.HC (Oe)                                                                           (BH)max (× 10.sup.6 G.Oe)                   ______________________________________                                        1         0       0         0                                                 2         200     50        0.0                                               3        1050     400       0.1                                               4        6200     2200      6.0                                               5        1500     700       0.4                                               6        4350     1700      3.8                                               7        1150     500       0.2                                               8        4900     1600      4.1                                               9        6300     2300      6.2                                               10       6400     2400      6.5                                               11       6250     2400      6.3                                               12       4300     1800      4.0                                               13       3350     2200      2.2                                               14       1200     550       0.3                                               15       4950     1850      4.3                                               16       6400     2400      6.5                                               17       6450     2550      6.8                                               18       6300     2500      6.4                                               19       5050     2350      4.7                                               20       1200     450       0.2                                               21       4050     1600      3.7                                               22       4800     1900      4.5                                               23       6500     2600      7.1                                               24       6450     2600      7.0                                               25       6300     2550      6.3                                               26       5350     2250      4.8                                               27       1150     600       0.3                                               28       4550     1700      4.0                                               29       4800     1950      4.2                                               30       6000     2400      5.9                                               31       6250     2450      6.4                                               32       6100     2400      6.0                                               33       5800     2350      5.5                                               34        800     450       0.1                                               35       1500     700       0.4                                               36       5950     2250      5.5                                               37       5700     2100      5.2                                               38       3300     2450      2.4                                               39       3350     2500      2.5                                               ______________________________________                                    

The results of examination of the phase structure as conducted by way ofX-ray diffraction, optical microscopy and electron microscopy were asfollows:

1. Tests specimens in which one of the AlMn(γ) phase or β-Mn phase, orboth, were recognized in large amounts included those of Nos. 1, 2, 3,5, 7, 14, 20, 27, 34 and 35, i.e., those test specimens of Mn being lessthan 68.0% or C less than 0.2%. From the result of X-ray diffraction ofthose test specimens, the amount of τ phase was found to haveappreciably decreased from those given in Table 9.

2. Test specimens in which Al₄ C₃ was recognized by optical microscopyincluded those of Nos. 2, 6, 12, 13, 19 and 26, i.e., those testspecimens with their compositions falling in the range of C exceeding(1/3 Mn -- 22.2)%.

These test specimens began decaying several days - several weeks later.In test specimens in which Al₄ C₃ existed, their plasticity declined,and the degree of anisotropization also diminished.

3. In test specimens other than those of (1) and (2) mentioned above,i.e., those test specimens of Nos. 4, 8, 9, 10, 11, 15, 16, 17, 18, 21,22, 23, 24, 25, 26, 28, 29, 30, 31, 32, 33, 36, 37, 38, and 39, on themain, only τ or τ_(c) phase was recognized.

4. In test pieces aforementioned in (3), Mn₃ AlC and/or face centeredcubic phase being similar thereto were found in test pieces of Nos. 4,9, 10, 11, 16, 17, 18, 23, 24, 25, 30, 31, 32, 33, 36, 37, 38, and 39,which have composition including an amount of carbon more than (1/10 Mn-- 6.6)% respectively, and it was recognized such a tendency that theamount of Mn₃ AlC and/or face-centered cubic phase being similar theretowere slightly greater than that existing in the test pieces before warmdeformation.

Similarly, in the composition range of Mn 68.0 - 70.5%, C(1/10 Mn --6.6) - (1/3 Mn -- 22.2)% and remainder Al, anisotropic magnets obtainedby plastically deforming the alloys in this example which were quenchedand tempered, were excellent in magnetic characteristics compared toanistropic magnets obtained by plastically deforming the alloys temperedafter M treatment mentioned in Example 11.

The cause of this is unknown, but in case of Example 11, it is surmisedthat slight presence of the AlMn(γ) phase reduces the degree ofanisotropization, because, in the composition range, AlMn(γ) phase couldbe found in the phase existing in test pieces of Example 11 beforeplastic deformation thereof, but could not be found in the phase of thisexample.

Also, in range of Mn 70.5 - 73.0%, C(1/10 Mn -- 6.6) - (1/3 Mn --22.2)%, the remainder being Al, the test pieces of this Example areslightly or not at all turned into anisotropic. It is considered thatthe reason for this is the presence of great quantities of spheroidizedMn₃ AlC, and few amount of lamellar Mn₃ AlC and/or face-centered cubicphase (the latter being similar thereto) exists in alloys before plasticdeformation thereof.

EXAMPLE 17

The test specimen of No. 23 of Example 16 was further tempered at 550°Cfor 30 - 240 minutes after having been extruded as in Example 16. Themagnetic characteristics in the extrusion direction obtained as theresult was as shown in Table 13.

Besides, in the case of varying the temperature for tempering, in thetemperature range of 480° - 750°C, magnetic characteristics thereof wereimproved more than just after extrusion by holding it under temperingconditions for a proper time.

                  Table 13                                                        ______________________________________                                             Tempering                                                                Code time length                                                                              Br (G)   B.sup.HC (Oe)                                                                         (BH)max                                           (min)                       (× 10.sup.6 G.Oe)                      ______________________________________                                        a    30         6600     2750    7.8                                          b    60         6600     2750    7.8                                          c     120       6500     2600    7.1                                          d     240       6150     2200    5.9                                          ______________________________________                                    

EXAMPLE 18

From the casting of No. 24 of Example 15, test specimens, each of 20 mmφ× 35 mm were cut out. They were tempered at 600°C for 30 minutes aftersubjecting them to a quenching similarly as in Example 15. Thereafter,one part was extruded at a pressure of 12.5 tons, using a die with asurface reduction percentage of 65% at a temperature of 730°C. Themagnetic characteristics in the extrusion direction were found to be:

    Br = 6450G .sub.B Hc = 2250 Oe (BH)max = 6.8 × 10.sup.6 G.Oe.

The other part was similarly extruded to a surface reduction percentageof 25% at 730°C, and then, was further extruded, so that the surfacereduction percentage would be 65% in total at the same temperature.

The magnetic characteristics in the extrusion direction after the secondextrusion was conducted were found to be:

    Br = 6450 G .sub.B Hc = 2600 Oe (BH).sub.max = 7.1 × 10.sup.6 G.Oe

The magnetic characteristics in the extrusion direction obtained byfurther subjecting the test specimen twice extrude to an annealing at550°C for 30 minutes, were found to be:

    Br = 6500 G .sub.b Hc = 2700 Oe (BH).sub.max = 7.5 × 10.sup.6 G.Oe.

A larger improvement was achieved in (BH)_(max) when the extrusion wasmade in more than 2 cycles than when it was conducted in 1 cycle.

EXAMPLE 19

The test specimen of No. 39 of Example 15 was extruded under the sameconditions as in Example 18.

After the extrusion to a surface reduction percentage of 65%, themagnetic characteristics both in the extrusion direction and in rightangles to the extrusion direction were:

    Br = 3300 G .sub.B Hc = 2450 Oe (BH).sub.max = 2.3 × 10.sup.6 G.Oe

The magnetic characteristics obtained after the second extrusion to atotal surface reduction percentage of 65% (the extrusion being conductedin the same way as in Example 18) both in the extrusion direction and inright angles to the extrusion direction, were:

    Br = 3350 G .sub.B Hc = 2400 G (BH).sub.max = 2.3 × 10.sup.6 G.Oe

The magnetic characteristics in the extruding direction of the testspecimen which had been subjected to the second extrusion, as obtainedafter further tempering it at 550°C for 30 minutes, were found to be:

    Br = 3200 G .sub.B Hc = 2200 Oe (BH).sub.max = 2.0 × 10.sup.6 G.Oe

EXAMPLE 20

A rod shape test specimen consisting of Mn 67.5 - 73.0%, C(1/5 Mn --13.3)±0.03% on the basis of the amount of Mn and the balance being Alwas cast similarly as in Example 15, and from this casting, acylindrical test piece of 20mm φ × 35mm was cut out. It was subjected tothe homogenization treatment and quenching, as in Example 15 and wasthen tempered at 600°C for 30 minutes. The test piece thus tempered wasextruded at 730°C by a pressure of 12.5 tons to a surface reductionpercentage of 75%.

For the test piece which had gone through the treatments mentionedabove, the relationship between the amount of Mn and the degree ofanisotropization was found to be as shown in FIG. 7. Thus, a very highdegree of anisotropization was achieved in the range of Mn being 68.0 --70.5%.

The degree of anisotropization was, as in the preceding description,expressed by the ratio of (BH)_(max) between the extruding direction,i.e., the axial direction of the test piece, and the direction at aright angle to the extruding direction, i.e., the direction of thediameter of the test piece.

EXAMPLE 21

From the casting of No. 24 of Example 15, a test piece of 20 mm φ × 35mmwas cut out. It was subjected to the homogenizing treatment andquenching similarly as in Example 15, and then, extruded by a pressureof 15 tons, using a die having a reduction percentage of 75% at 700°Ctheirafter tempered at 600°C for 30 minutes. The magneticcharacteristics in the extruding direction of the test piece obtained inthis way were found to be:

    Br = 6600 G .sub.B Hc = 2300 Oe (BH).sub.max = 6.8 × 10.sup.6 G.Oe

EXAMPLE 22

From the casting of No. 10 of Example 15, a test piece of 20mm φ × 35mmwas cut out. It was tempered at 550°C for 30 minutes after subjecting itto the homogenization treatment and quenching similarly as in Example15, and was then, upset, using a die of 40mm φ at 750°C. The test pieceof 40mm φ × 8.8mm formed showed no crack at all. From the outerperipheral part of this test piece, a cube of 8.8 × 8.8 × 8.8 mm was cutout. By the measurement of its magnetic characteristics, it was foundout to be an anisotropic magnet with its preferred direction ofmagnetization in its diameter direction. The magnetic characteristics inthe preferred direction of magnetization observed were:

    Br = 5500 G .sub.B Hc = 2400 Oe (BH).sub.max = 5.3 × 10.sup.6 G.Oe.

By plastic deformation, magnetic anisotropization and formation intopredetermined shape are carried out at same time.

EXAMPLE 23

A square pillar shape test piece of 30 × 30 × 150 mm having acomposition ratio of Mn 69.28%, Al 30.28% and C 0.49%, as chemicallyanalyzed, was cast. After subjecting it to a homogenization at 1,150°Cfor 2 hours, it was quenched from 1,000°C to 600°C at a cooling rate ofabout 400°C/min., and was then, tempered at 600°C for 30 minutes. Thistest piece was rolled in 5 cycles to a thickness of 10 mm on groovedrolls of 30 mm groove width without crack.

The formed test piece turned out to be an anisotropic magnet with itspreferred direction of magnetization in the rolling direction, and itsmagnetic characteristics in its preferred direction of magnetizationwere found to be:

    Br = 6450 G .sub.B.sup.H c = 2500 Oe (BH).sub.max = 6.6 × 10.sup.6 G.Oe.

EXAMPLE 24

From the casting of No.16 of Example 15, a cylindrical test piece of20mmφ × 35mm was cut out. It was subjected to the homogenization andquenching similarly as in Example 15, and was then, extruded at 700°Cand at a pressure of 12.5 tons, while applying a magnetic field of 3,000Oe in the extrusion direction by use of a solenoid and was then temperedat 600°C for 30 minutes. The test piece obtained in this way turned outto be an anisotropic magnet with its preferred direction ofmagnetization in the extruding direction. The magnetic characteristicsin the extrusion direction were found to be:

    Br = G .sub.B Hc = 2250 Oe (BH).sub.max = 6.8 × 10.sup.6 G.Oe

EXAMPLE 25

From the casting of No. 10 of Example 15, a test piece of 10mmφ × 20mmwas cut out. It was tempered at 600°C for 30 minutes after subjecting itto the homogenization treatment and quenching similarly as in Example15. It was then, extruded at 700°C, using a die having reductionpercentage of 75%, with an ultrasonic vibration applied either on thedie or punch, while making the extrusion.

The magnetic characteristics observed in the extruding direction when avibration of 27 KHz was applied were:

    Br = 6350 G .sub.B Hc = 2600 Oe (BH).sub.max = 6.8 × 10.sup.6 G.Oe

EXAMPLE 26

From the casting of No. 16 of Example 15, a test piece of 10 mmφ × 20mmwas cut out. It was tempered at 600°C for 1 hour after subjecting it tothe homogenizing treatment and quenching similarly as in Example 15, andwas then, extruded at a high speed at 750°C, using a die having areduction percentage of 75%. When the extrusion speed was 10 m/sec., themagnetic characteristics in the extrusion direction were found to be:

    Br = 6200 G .sub.B Hc = 2600 Oe (BH).sub.max = 6.4 × 10.sup.4 G.Oe.

The test piece could be formed without crack.

EXAMPLE 27

The mechanical properties of the conventional isotropic Mn-Al-C magnetswere superior to those of the Mn-Al magnets, but they could be machinedon lathes, etc., only with difficulty, their mechanical strength lyingat such a low level as tensile strength 2 kg/mm², elongation 0 andtransverse strength 7 kg/mm².

On the other hand, in the test pieces after having undergone therespective treatments of each embodiment of this invention described inthe foregoing, had mechanical strengths which were remarkably improved,reaching high levels such as tensile strength 20 - 30 kg/mm², elongation3 - 5% and transverse strength 30 - 40 kg/mm², and because of theirhighly improved machinability, such machining treatments as ordinarylathing, drilling by use of drilling machines etc., could be performedwith ease even in their state of being magnetized.

EXAMPLE 28

A rod shape casting of an Mn-Al alloy having a composition of Mn 71.62%and Al 28.38%, as chemically analyzed, was manufactured by way ofmelting and casting. From this casting, a cylindrical test piece of20mmφ× 36mm was cut out, and after holding it at a temperature of1,000°C for 1 hour, was quenched into water. The test piece after beingquenched showed a development of numerous cracks. The test piece afterbeing quenched, was examined by way of X-ray diffraction as to its phasestructure, and was found to be in the ε phase only.

This cylindrical test piece in the ε phase was compressed to a degree ofdeformation of -50% by applying a pressuring force of 45 kg/mm² at atemperature of 650°C in the axial direction of its cylinder. The testpiece after being compressed was found to be isotropic, giving lowmagnetic characteristics as:

    Br = 1,300 G .sub.B Hc = 800 Oe (BH).sub.max = 0.3 × 10.sup.6 G.Oe.

The test piece after compression, was examined by X-ray diffraction andshowed the existence of the β-Mn phase and AlMn(γ) phase in abundance.

And then from a rod shape casting of a Mn-Al alloy having a compositionof Mn 69.05% and Al 30.96%, as chemically analyzed, a cylindrical testpiece of 20mmφ × 35mm was cut out. The test piece was quenched intowater after holding it at 1,000°C for 1 hour. The phase structure of thetest piece which had been quenched into water was found to be in the εsingle phase, as determined by X-ray diffraction. It was tempered intothe τ phase, and was, then, extruded at 650°C by a pressure of 16 tonsto a reduction percentage of 64%. The test piece formed was isotropic,and its magnetic characteristics were found to be:

    Br =  900 G .sub.B Hc =  450 Oe (BH).sub.max = 0.1 × 10.sup.6 G.Oe.

As revealed by the X-ray diffraction of the test piece after having beentreated, large amounts of β-Mn phase and AlMn(γ) phase were recognized,but the τ phase was found only in a very small amount.

Furthermore, the results were nearly the same when the composition of Mnand Al, the condition of heat treatment and the conditions of treatmentswere altered; it was impossible to achieve a magnetic characteristic of(BH)_(max) above 1.0 × 10⁶ G.Oe, and its mechanical strength was termedvery brittle.

As described hereinabove, the Mn-Al alloys, the stability of the δ phaseand τ phase was not only lower then in the Mn-Al-C alloys containing anamounts of carbon in excess of its solubility limit, but the straininduced transformation was promoted when the treatment was performed intemperature ranges above 530°C, so that it was virtually impossible topreserve the τ phase, and moreover, anisotropization was not obtainedbecause of absence of the orientation control effect whereby the degreeof orientation increases by the presence of lamellar Mn₃ AlC phase.

EXAMPLE 29

A similar experiment to those of Examples 11, 14 and 16 was carried outwith an Mn-Al-C-X alloy(s) manufactured by adding an additive element(s)X to the Mn-Al-C alloy.

An Mn-Al-C-Nb alloy in the shape of a cylinder of 20mmφ× 35mm having acomposition of Mn 71.47%, Al 25.06%, C 1.03% and Nb 2.44%, as chemicallyanalyzed, with Nb chosen as X, was manufactured melting, casting andheat treatment in a manner similar to that of Example 11. This alloy,was determined by X-ray diffraction and optical microscopy to be mainlyin the τ_(c) (M) phase.

As this test piece was compressed to a degree of deformation of -65% inthe axial direction of its cylinder under a pressure of 45 kg/mm² andtemperature of 680°C. The test piece after being worked on wasidentified as an anisotropic magnet with its preferred direction ofmagnetization in the diameter direction, having the following magneticcharacteristics in that direction:

    Br = 5,200 G .sub.B Hc = 2,800 Oe (BH).sub.max = 4.9 × 10.sup.6 G.Oe

Thus, an improvement in (BH)_(max) was recognized over the magneticcharacteristic obtained in the similar experiment with an Mn-Al-C alloyof Example 11.

Next, a cylindrical Mn-Al-C-Nb alloy of 20mmφ × 35mm consisting of Mn69.69%, Al 21.14%, C 0.72% and Nb 0.56% in the composition ratio, aschemically analyzed, with Nb chosen as X, was melted, and cast, andthen, subjected to the homogenization and quenching in the same way asin Example 15. This test piece was tempered at 600°C for 30 minutes.Then, as its phase structure was examined by X-ray diffraction, theAlMn(γ) phase and β-Mn phase were not recognized, but mainly the τ phaseonly was detected.

When this test piece was extruded at 700°C by a pressure of 15 tons tothe reduction percentage 75%, the test piece formed turned out to be ananisotropic magnet with its preferred direction of magnetization in theextrusion direction. Its magnetic characteristics in the preferreddirection of magnetization were found to be:

    Br = 6200 G .sub.B Hc = 2600 Oe (BH).sub.max = 6.7 × 10.sup.6 G.Oe.

This shows an improvement in (BH)_(max) over the result with the testpiece of No. 31 of Example 16.

In the next place, various Mn-Al-C-X alloys in which such additiveelements X as B, N, Ti, Pd, Bi, V, Ag, Fe, Mo, Ni, Ge, Nb, Co, Pb, Zn,S, Ce and Sm, were added, singly or in combination of more than 2 ofthem, at weight ratios within 6, with the Mn-Al-C alloys as 100 havingtheir composition falling within

    Mn       68.0˜73.0%                                                     C        (1/10Mn - 6.6)% ˜ (1/3Mn - 22.2)%                              Al       remainder                                                        

were manufactured, and with these alloys, similar experiments as thoseof Examples 11, 14 and 16 were conducted. The results were especiallynotable in that the Mn-Al-C-(Nb×Mo) alloy with a 2.0% Nb and a 0.5% Moweight ratio showed an improvement of about 10% in (BH)_(max) over theresults in the cases of Examples 11 and 14, and also in Mn-Al-C-X alloyscontaining the additive elements of B, Ti, Fe, Mo, Ge, Co, Ni and Nbsingly or in combination of more than 2, upgradings in magneticcharacteristics were noted.

Furthermore, in Mn-Al-C-Pb alloys with Pb added in 3.0 by weight ratio,their magnetic characteristics were found nearly equal or somewhatinferior to those obtained in Examples 11 and 14, but their plasticitywas notably better. Such a tendency was observed also in Mn-Al-C-Znalloys containing Zn as the additive.

Also, improved magnetic characteristics were observed in Mn-Al-C-B-Tialloys with an 0.2% Ti and 0.3% B weight ratio, i.e. the (BH)_(max) wasimproved by about 10 percent over that of the alloy of Example 16. Andalso, in Mn-Al-C-X alloys containing additive elements of B, Ti, Ni, Fe,Mo, Ge, Nb and Co, added singly or in combination within 3 by weightratio to Mn-Al-C alloy as 100, improved magnetic characteristics wererecognized.

Furthermore, in Mn-Al-C-Pb alloys with Pb added 2.0% in weight ratio,their magnetic characteristics were nearly equal to or slightly lessthan those of Example 16, but they had notably enhanced plasticity. Sucha tendency was observed also were Zn was added, i.e. Mn-Al-C-Zn alloys.

As clarified by various examples described hereinabove, the abnormallylarge plasticity at 530°- 830°C of the Mn-Al-C alloys consisting of Mn68.0 - 73.0%, C(1/10Mn -- 6.6)% - (1/3Mn -- 22.2)% and remainder Al isbased on the phasal transformation of ε_(c) → ε_(c) ' ⃡ τ_(c) inductedby the plastic deformation and especially on the abnormally largeanisotropic plasticity of the ε'_(c) phase. The phenomenon of thisabnormal plasticity is called transformation plasticity. The notableanisotropization effected by the warm plastic deformation making use ofthis transformation plasticity results from the sliding of the plane ofatoms on each of the following crystal plane:

    ε.sub.c (0001)// ε'.sub.c (100)// τ.sub.c (111),

Particularly in the direction toward [001]on the ε'_(c) (100) plane,which accompanies the above described phase transformation, as detailedwith regard to the machanisms of deformation, transformation andmagnetism in Examples 3, 4 and 5. Accordingly, by having the lamellarMn₃ AlC phase on the ε_(c) (0001) plane, it is possible to give priorityto the desirable sliding of the plane of atoms on the aforementionedcrystal planes, so that the degree of anisotropization may be notablyincreased by taking advantage of that orientation controlling effect ofthe lamellar Mn₃ AlC.

The present invention relate to anisotropic Mn-Al-C alloys obtained bysubjecting the alloys having compositions within the ranges enclosed bythe lines connecting the points A, B, C and D, as represented in theMn-Al-C ternary diagram of FIG. 8, that is the composition range of Mn68.0 - 73.0%, C(1/10 Mn -- 6.6) - (1/3 Mn -- 22.2)% and remainder Al, bysubjecting them to transformation plasticity based on the phasetransformation at 530°- 830°C.

Particularly, in the composition range enclosed by lines connecting thepoints E, F, C and D as shown in the diagram of FIG. 8, that is thecomposition range of Mn 70.5-73.0%, C(1/10Mn -- 6.6) - (1/3Mn -- 22.2)%,and remainder Al, by separating the lamellar Mn₃ AlC phase before warmplastic deformation, the degree of anisotropization mentioned above maybe remarkably increased.

Moreover, in the composition range enclosed by lines connecting thepoints A, B, F, and E as shown in the diagram of FIG. 8, that is thecomposition range of Mn 68.0 - 70.5%, C(1/10Mn -- 6.6) - (1/3Mn --22.2)% and remainder Al, by warm plastic deformation of the alloyincluding phase, particularly the phase having adequate amount of Cobtained by heat treatment, a magnet having very high degree ofanistropization and having excellent magnetic characteristics may beobtained.

Although the mechanisms regarding polycrystals can hardly be clarifiedquantitatively, various phenomena described in the aforementionedExamples may be interpreted qualitatively by the similar mechanisms ofdeformation, transformation and magnetism as those of monocrystals.Thus, because polycrystals generally require the deformation needed forthe rotation and movement of the grain boundary, in addition to theanisotropic deformation in each crystal grain, they must be worked on toa greater extent than monocrystals. Moreover, their magneticcharacteristics are improved at a degree of deformation of 30 - 65%; andbecause of their being polycrystalline, the degrees of anisotropizationattained with them are 30 - 40% smaller than those with monocrystals,but the composition range, phase structure and the deforming temperaturerange required for the realization of the above described phenomena wereconfirmed to be really the common essentials. And then, it wasconsidered that mechanism of anisotropization is not only based ontexture induced by working.

That the existence of carbon in excess of its solubility limit and thestate of its existence are among the important indispensable factors inattaining such unexpectedly notable anisotropization as above describedbased on the mechanisms of deformation, transformation and magnetism,was definitely indicated by various examples hereabove described.

According to this invention, mechanical strengths of anisotropic magnetsgiving very high degrees of anisotropization with (BH)_(max) runningfrom 4.8 - 9.2 × 10⁶ G.Oe, were 4 - 10 times as high as those ofconventional Mn-Al-C magnets; they had such high toughness that theycould be subjected to such machining as the ordinary lathing; excelledin weather resistance, corrosion resistance, stability and temperaturecharacteristics, and they were thus of high industrial value.

Furthermore, this invention has made it possible to apply not only theextrusion and compression, but all other plastic deformation, as well,including, for example, the wire drawing, drawing, rolling die rolling,die upsetting, etc., and accordingly, while opening the way for thepossibility of cutting the workpieces magnetized, it providesanisotropic magnets with their preferred direction of magnetization inany arbitrary directions in desired shape.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. An anisotropic permanentmagnet of an alloy which comprises 68.0 to 73.0 % by weight ofmanganese, carbon in an amount between the solubility limit and(1/3Mn--22.2)% and the remainder being aluminum, said alloy having beensubjected to warm plastic deformation and wherein the anisotropicpermanent magnet exhibits magnetic properties such that the (BH)max isabove 4.8 × 10⁶ G.Oe in its bulk state, and is further characterized inbeing machinable.
 2. An anisotropic permanent magnet of an alloy whichcomprises 68.0 to 73.0 % by weight of manganese, carbon in amountsranging from (1/10Mn--6.6)% to (1/3Mn--22.2)% and the remainder beingaluminum, said alloy having been subjected to warm plastic deformationand wherein the anisotropic permanent magnet exhibits magneticproperties such that the (BH)max is above 4.8 × 10⁶ G.Oe in its bulkstate, and is further characterized in being machinable.
 3. Ananisotropic permanent magnet according to claim 2, wherein manganese ispresent in amounts between 68.0% to 70.5% by weight.
 4. An anisotropicpermanent magnet according to claim 2, wherein the alloy contains thecompound Mn₃ AlC therein.
 5. An anisotropic permanent magnet accordingto claim 2, wherein the alloy contains manganese in an amount of 70.5%to 72.5% and which also contains the compound Mn₃ AlC therein.
 6. Ananisotropic permanent magnet according to claim 2, wherein the alloyfurther contains at least one or more additive elements selected fromthe group of Nb, Mo, B, Ti, Fe, Ge, Ni and Co in an effective amount upto 6 wt. parts based on 100 parts of the manganese-aluminum-carbon alloyto increase the (BH)max value of the alloy defined in claim
 2. 7. Ananisotropic permanent magnet according to claim 2, wherein the alloyfurther contains one or two additive elements selected from the groupconsisting of Pb and Zn in an effective amount up to 6 wt. parts basedon 100 parts of the manganese-aluminum-carbon alloy to increase theplasticity of the alloy defined in claim 27.